ORDER

NEIL WAKE, District Judge

The court has considered Defendant Lake Havasu City's Motion for Summary Judgment (doc. # 69), Defendant Mohave County's Motion for Summary Judgment (doc. # 66) and Lake Havasu City's Motion to Exclude Testimony of Plaintiffs' Expert David Penney (doc. # 68).

Plaintiffs Christopher Heck, Lisa Castillo, and Sandra Ballew ("Plaintiffs") brought this action against the City of Lake Havasu and Mohave County, Arizona ("Defendants") alleging negligence, gross negligence, and "dangerous condition of public property" in connection with the death of Timothy Heck. Timothy Heck died in the Bridgewater Channel (the "Channel") at Lake Havasu, Arizona, on Sunday, August 31, 2003. According to Plaintiffs, Timothy Heck passed out and drowned while swimming due to the high levels of carbon monoxide emitted from boats in the Channel. Plaintiffs allege that the City of Lake Havasu (the "City") and County of Mohave (the "County") knew about this hazard but failed to remedy it. The City and County now move for summary judgment.

I. Legal Standard

Rule 56 of the Federal Rules of Civil Procedure provides that summary judgment shall be entered if the pleadings, depositions, affidavits, answers to interrogatories, and admissions on file show that there is no genuine dispute regarding the material facts of the case and the moving party is entitled to a judgment as a matter of law. See Fed.R.Civ.P. 56(c) (2004); Anderson v. Liberty Lobby, Inc., 477 U.S. 242, 247 (1986). The Court must evaluate a party's motion for summary judgment construing the alleged facts with all reasonable inferences favoring the nonmoving party. See Baldwin v. Trailer Inns, Inc., 266 F.3d 1104, 1117 (9th Cir. 2001).

The party seeking summary judgment bears the initial burden of informing the Court of the basis for its motion and identifying those portions of the pleadings, depositions, answers to interrogatories, and admissions on file, together with the affidavits, if any, which it believes demonstrate the absence of any genuine issue of material fact. See Celotex Corp. v. Catrett, 477 U.S. 317, 323 (1986). Where the moving party has met its initial burden with a properly supported motion, the party opposing the motion "may not rest upon the mere allegations or denials of his pleading, but . . . must set forth specific facts showing that there is a genuine issue for trial." Anderson, 477 U.S. at 248. Summary judgment is appropriate against a party who "fails to make a showing sufficient to establish the existence of an element essential to that party's case, and on which that party will bear the burden of proof at trial." Id. at 322. See also Citadel Holding Corp. v. Roven, 26 F.3d 960, 964 (9th Cir. 1994). Although the initial burden is on the movant to show the absence of a genuine issue of material fact, this burden may be discharged by indicating to the Court that there is an absence of evidence to support the nonmoving party's claims. Daubert v. Merrell Dow Pharm., Inc., 43 F.3d 1311, 1315 (9th Cir. 1995).

II. Background

Visitors come to the channels around Lake Havasu to enjoy the sun, swim, relax, and socialize. On busy summer weekends, boats squeeze in next to each other lining the Channel, often with the owners leaving their boats on idle or intermittently turning them on to recharge the batteries. (Doc. # 70 Ex. 1.) In the water around and behind the boats, visitors toss footballs, wade, play games, and drink beers.

These gatherings, unfortunately, present an invisible risk. A boat emits about the same amount of carbon monoxide per minute as 188 cars. (Doc. # 70 Ex. 14 at 0011.) As well as the potential longer-term harms of carbon monoxide, the colorless and odorless gas can cause nausea, headache and fatigue at lower doses and unconsciousness or death at higher ones. (Doc. # 70 Ex. 14 at 0011.) Most problematically, the effects of carbon monoxide poisoning parallel the effects of excessive drinking and heat exposure, both of which are common in the channels around Lake Havasu during Arizona's summertime. Additionally, alcohol consumption reduces a person's ability to resist carbon monoxide. (Doc. # 90 Ex. 17 at ln 21-22.)

A. The Danger

Plaintiffs present evidence of seven specific instances of carbon monoxide poisoning in Lake Havasu and the Channel which they claim should have placed Defendants on notice of the problem. Four cases involved passengers on boats becoming sick or passing out (doc. # 86 at ¶¶ 18, 20, 21, 28), and the other three involved swimming deaths. In May of 2001, 2002, and 2003, visitors to Lake Havasu and the Channel drowned, at least in part due to carbon monoxide exposure. ( Id. at ¶¶ 19, 26, 29.)

By December of 2002, carbon monoxide poisoning had become somewhat of a concern for physicians in Lake Havasu's hospital. Since 2000, Dr. Ward and his colleagues at the Havasu Regional Medical Center had noticed patients coming into the Emergency Room with carbon monoxide poisoning. (Doc. # 86 at ¶¶ 33-34.) Dr. Ward spoke with the City's EMS Coordinator for the fire department, Frank Foti, and Foti told Ward that Foti had suggested to his superiors that the National Institute for Occupational Safety and Health ("NIOSH") be invited to Lake Havasu to do carbon monoxide testing. (Doc. # 86 Ex. 19 at 18:4-11.) Because Foti indicated that his idea had been refused ( id.), Dr. Ward himself invited Jane McCammon from NIOSH to come out and do some preliminary testing. (Doc. # 86 Ex. 19 at 19:14-25.) The results were significant. ( Id. at 21:1-16.) On December 10, 2002, Dr. Ward wrote a letter to the Mayor and City Manager with the NIOSH report attached. (Doc. # 86 at ¶ 38.) He never received a response. ( Id. at ¶ 40.) Dr. Ward therefore sent the report to a local newspaper, which published the findings on February 6, 2003. ( Id. at ¶¶ 41-42; Ex. 22.)

B. The City's Actions

Before the article was published, upon receiving Dr. Ward's letter, Lake Havasu's City Council decided to research environmental consulting firms to hire one to gather empirical data on the problem. (Doc. # 70 Ex. 7 at 48:16-50:19.) The City also began testing its employees for carbon monoxide exposure and rotating employees on two-hour shifts to reduce their exposure levels. ( Id.) After the article's publication, on April 8, 2003, the City Council revisited the carbon monoxide issue. (Doc. # 86 Ex. 24 at 0003-0005.) The Council decided at that time to hire the environmental consulting firm Sonoma Technologies, Inc., to perform an initial "scoping study." ( Id.) The "scoping study" would evaluate the NIOSH report and other available data and make recommendations. (Doc. # 70 Ex. 13 at 0007.) The City Council also debated at that time whether to immediately begin posting warning signs. (Doc. # 86 Ex. 24 at 0003-0005.) However, due to uncertainty about the extent of the problem and what the best solution might be, the Council decided to obtain empirical information first and not "rush to solutions." ( Id.)

In May of 2003, the Council met again and heard testimony from Dr. Ward and experts on carbon monoxide. (Doc. # 70 Ex. 14 at 0010-0017.) The Council decided to authorize $50,000 for a comprehensive study by Sonoma Technologies and, due to concerns that Memorial Day weekend and the summer were quickly approaching, to have City employees post signs regarding the hazard. ( Id. at 0015, 0017.) On June 10, 2003, the City revised the scope of work being done by Sonoma Technologies to include a $13,000 public informational campaign. (Doc. # 70 Ex. 15 at 0024-0025.)

C. The County's Actions

In response to the article, the County Board of Supervisors discussed the issue. (Doc. # 67 Ex. 8 at 0090-0091.) In light of the air testing planned by the City, and because the Board, like the City Council, felt that more information was necessary, it decided to take no action. ( Id.; see also id. at Ex. 7 at 1.)

D. Timothy Heck's Death

Timothy Heck came to Lake Havasu with his brother and three friends in 2003 over Labor Day weekend. (Doc. # 86 at ¶ 47.) It was Timothy's birthday, and the four of them came to stay with another friend who owned a house and boat in the City. ( Id. at ¶ 49.) On Sunday, August 31, 2003, the group was on the water by 9:00 a.m. ( Id. at ¶ 50.) Shortly after 10:00 a.m., three of them walked to Walgreens to buy Gatorade and beer. ( Id. at ¶ 51.) At around 2:00 p.m., Timothy and his friends were hanging out in the water behind their boat and socializing when Timothy left to get something to drink. ( Id. at ¶¶ 54-57.) Timothy did not appear intoxicated at the time. ( Id. at ¶ 65.) At around 2:30, Ray Miranda, one of Timothy's friends, began to feel ill in a way he had never felt before. ( Id. at ¶¶ 58-59.) After Timothy failed to return, his friends began to look for him. ( See id. at ¶ 60.) They were unable to find him.

The next morning, the Lake Havasu Police Department informed the group that a body, later identified as Timothy, had been found by a diver at the bottom of the Channel. ( Id. at ¶ 61.) The body was found in approximately eight feet of water about 30 feet from the shoreline. (Doc. # 86 Ex. 33 at 1.) The County Medical Examiner, Dr. Nelson, performed an autopsy and drew a blood sample to test for alcohol and carbon monoxide. (Doc. # 86 at ¶¶ 66-67.) The autopsy revealed a hematoma on Timothy's head of up to ten centimeters and a "red/blue livor involving the anterior aspect of the face and upper chest." (Doc. # 86 Ex. 32 at 4.) The trauma to the head, if it occurred while Timothy was alive, would not likely have killed him but could have contributed to his drowning. (Doc. # 84 at ¶ 55.) Additionally, a reddish fluid was present in both nostrils and the mouth, and a "reddish/pink fluid" was found in the trachea and larynx. (Doc. # 86 Ex. 32 at 4, 6.) The blood sample was destroyed by the laboratory in a mix-up, preventing ascertainment of Timonthy's precise carbon monoxide level at the time of death without exhuming the body. (Doc. # 86 Ex. 33 at 1-3.)

E. Postscript

Upon completion of Sonoma Technologies' investigation, the City passed an "Engines Off" ordinance preventing boats from idling while beached in the Channel and an ordinance giving the Police Chief discretion to close the Channel when air quality deteriorates. (Doc. # 70 Ex. 16 at 0058.) The City also authorized money to be spent on pamphlets, posters, public awareness announcements and signs, as well as a city employee education and monitoring program. ( Id.)

III. Analysis

Defendants argue, and Plaintiffs concede, that Arizona law does not formally recognize a separate tort of "dangerous condition of public property." (Doc. # 85 at 16.) Defendants challenge Plaintiffs' remaining claims of negligence and gross negligence on the grounds (A) that no duty was owed to Timothy Heck, (B) that Plaintiffs have no admissible evidence of causation, and (C) that the claims are barred by statutory immunity.

A. Duty

"[A] negligence action may be maintained only if there is a duty or obligation, recognized by law, which requires the defendant to conform to a particular standard of conduct in order to protect others against unreasonable risks of harm." Markowitz v. Ariz. Parks Bd., 146 Ariz. 352, 355, 706 P.2d 364, 367 (1985) (citations omitted). In Arizona, the relationship of the parties determines whether a duty exists. Id. As explained by the Arizona Supreme Court in Coburn v. City of Tucson, 143 Ariz. 50, 51-52, 691 P.2d 1078, 1079-80 (1984):

Many tort decisions exhibit an unfortunate tendency to confuse the concepts of `duty' and standard of conduct and to argue that the city is, or is not, under a duty to post warning signs, remove obstructions from the road or sidewalks, install traffic control devices, fix potholes, and the like. We believe that an attempt to equate the concept of `duty' with such specific details of conduct is unwise. . . . It is better to reserve `duty' for the problem of the relation between individuals which imposes upon one a legal obligation for the benefit of the other, and to deal with particular conduct in terms of a legal standard of what is required to meet the obligation. . . . What the defendant must do, or must not do, is a question of the standard of conduct required to satisfy the duty.

(Citations omitted). As a general matter, the question of whether a duty existed is one for the court. Markowitz, 146 Ariz. at 355, 706 P.2d at 367.

Plaintiffs argue (1) that the City and County had a duty to Timothy Heck arising from their relationship and (2) that the County also had a duty to Heck arising from statute.

1. Relationship-Created Duty

Plaintiffs argue that the relationship between the Defendants, as possessors of the Channel, and Timothy Heck, as an invitee, gave rise to a duty to warn or protect Heck from unreasonable dangers in the Channel. "Arizona recognizes that a possessor of land is under an affirmative duty to use reasonable care to make the premises safe for use by invitees." Markowitz, 146 Ariz. at 355, 706 P.2d at 367 (citations and internal quotations omitted). This duty applies equally to government possessors and those persons the government invites to use the land for recreational purposes. Id. at 356-57, at 369-370 (holding that the State of Arizona, as then-possessor of Lake Havasu, owed a duty of reasonable care to a recreational invitee at the lake involved in a diving accident); see also Bellezzo v. State of Arizona, 174 Ariz. 548, 551, n. 4, 851 P.2d 847, 850, n. 4 (App. 1992) (holding that because plaintiff was an invitee to the State's baseball stadium the State had a duty to warn or protect plaintiff against unreasonable risks of harm therein). Defendants therefore owed a duty of care to Timothy Heck if (i) they "possessed" the Channel and (ii) Heck was an "invitee."

i. Possession

A "possessor" of land is defined as "a person who is in occupation of the land with intent to control it." Clarke v. Edging, 20 Ariz. App. 267, 272, 512 P.2d 30, 35 (App. 1973) (citing Restatement (Second) of Torts § 328E). However, the Arizona cases treat control exercised over the land as dispositive in determining whether a defendant owes a duty as a possessor. E.g., Siddons v. Bus. Props. Dev. Co., 191 Ariz. 158, 158-59, 953 P.2d 902, 902-903 (1998) (inquiring whether landlord exercised "dominion and control" over the sidewalk where the harm occurred such that the landlord would owe a duty as possessor); Sanchez v. City of Tucson, 191 Ariz. 128, 130-31, 953 P.2d 168, 170-71 (1998) ("[I]f the City exercised control over the roadway in question, it would owe a duty to the plaintiff to keep it in a reasonably safe condition." (citations omitted)). Whether a defendant exercised control over a parcel of land is a question of fact ordinarily left to the factfinder. Sanchez, 191 Ariz. at 130, 953 P.2d at 170; see also Siddons, 191 Ariz. at 159, 953 P.2d at 903. Where multiple governmental entities exert different levels of "joint control" over the land, each may have a duty, and any potential liability may be apportioned between them. Sanchez, 191 Ariz. at 132-33, 953 P.2d at 172-73 (holding where state and city both exercised control over a roadway that liability for negligently failing to install a traffic light could be apportioned between them). Moreover, a government entity's exercise of control will give rise to a duty as possessor regardless of whether the government entity had the legal right to control the land. Id. at 131-33, at 171-73 (treating intergovernmental contract as merely part of the evidence to be submitted to the jury on the issue of control and rejecting the dissent's position that "legal" control should be dispositive); id. at 132, at 172 ("Even if a jury finds that the City had no right to exercise control under the [Intergovernmental Agreement], it could alternatively find that the City in fact exercised control over the roadway. . . ." (citations omitted)).

Plaintiffs have submitted admissible evidence raising a triable issue as to whether the City was a "possessor" of the Channel. On September 25, 2001, the State of Arizona quitclaimed the Channel to the City. (Doc. # 86 Ex. 1.) The City formally accepted the conveyance. (Doc. # 86 Ex. 2.) Moreover, County Supervisor Buster Johnson testified that the City owns, maintains and controls the Channel. (Doc. # 86 Ex. 3 at 51:15-52:25.)

On the other hand, Plaintiffs have failed to raise a triable issue as to whether the County was a "possessor." In opposition to the County's motion, Plaintiffs submit the testimony of former Mayor Robert Whelan that the County has authority to enforce rules, regulations, and ordinances that apply to the channel. (Doc. # 84 Ex. 3 at 37:17-38:13.) This and other testimony suggesting that the County exercises law enforcement authority over the Channel and the entire lake (doc. # 84 Ex. 3 at 37:17-38:13, 39:24-40:14), does nothing to demonstrate that the County occupies the Channel or intends to control it. The County's primary law enforcement authority extends throughout the unincorporated area of the County. Because Plaintiffs have not shown that the County exercises "dominion and control" over the Channel, Siddons, 191 Ariz. at 158-59, 953 P.2d at 902-903, as opposed to merely law enforcement authority, the County had no relational duty to Timothy Heck.

ii. Timothy Heck as "Invitee"

Under Arizona law, Timothy Heck was an "invitee" to the Channel. "A public invitee is defined as `a person who is invited to enter or remain on land as a member of the public for a purpose for which the land is held open to the public.'" Callender v. MCO Props., 180 Ariz. 435, 442, 885 P.2d 123, 130 (App. 1994) (citing Nicoletti v. Westcor, Inc., 131 Ariz. 140, 143, 639 P.2d 330, 333 (1982)). Where the government owns land that is open to the public, no express invitation is required for a user thereof to be classified as an invitee. See id. (holding that the plaintiff was a public invitee at the lake because the lake was "owned by the federal government and was open to the public"). Given that the Channel was held open to the public by the City, Heck is properly classified as a public invitee.

Plaintiffs have therefore shown a triable issue with regard to whether the City had a duty to Timothy Heck.

2. Statutory Duty of the County

Plaintiffs next argue that Arizona statutes imposed a duty on behalf of the County, pointing to two specific provisions. The first is a grant of authority to the County to pass ordinances reducing carbon monoxide levels. Section 11-251, A.R.S., provides:

The [county] board of supervisors, under such limitations and restrictions as are prescribed by law, may:

. . .

52. Make and enforce ordinances that are more restrictive than state requirements to reduce or encourage the reduction of carbon monoxide and ozone levels, provided an ordinance does not establish a standard for vehicular emissions, including ordinances to reduce or encourage the reduction of the commuter use of motor vehicles by employees of the county and employees whose place of employment is in unincorporated areas of the county.

This provision is plainly a grant of authority and saddles the County with no obligation to enact such ordinances. Compare Daggett v. County of Maricopa, 160 Ariz. 80, 82-84, 770 P.2d 384, 386-388 (App. 1989) (holding that regulations imposed duty on health department, running to the customers of a water amusement park, where the regulations provided that "Inspections of public and semi-public bathing places shall be made by representatives of the State or County Health Departments. . . ." (emphasis added)).

The second statute requires in the broadest of terms that the board of health of each Arizona county make rules and regulations for the benefit of public health. Section 36-184(B), A.R.S., states: "The board shall: . . . 3. Make rules and regulations, not inconsistent with the rules and regulations of the department of health services, for the protection and preservation of public health." Such sweeping language does not create a tort duty on behalf of the County running to every individual for every health hazard in society. Although Arizona cases have found a duty running to certain members of the public created by some statutes requiring local governments to regulate a field of societal activity, the field of activity placed under the local government's control by such a statute must at least be finite. See, e.g., Daggett, 160 Ariz. at 83, 770 P.2d at 387 (holding that regulations requiring government to inspect swimming areas created duty running to the customers of the water park); Bischofshausen v. Pinal-Gila Counties Air Quality Control Dist., 138 Ariz. 109, 111, 673 P.2d 307, 309 (App. 1983) (holding that Control District had duty to those harmed by its failure to properly regulate the asbestos mines and mills). Imposing a duty on the County Health Department here would leave it open to lawsuit for every health harm of every kind occasioned upon anyone in the County.

Although the County owed no duty to Timothy Heck, the Court addresses the remaining issues related to the County on these motions because they are relevant to the City as well.

B. Causation

Because nobody witnessed the drowning and because there is no blood toxicology report attesting to the level of carbon monoxide in Heck's blood at the time of his death, Plaintiffs rely on the opinion of an expert, Dr. David Penney, to establish that Heck's death was caused by carbon monoxide. The court therefore first addresses the motion to exclude Dr. Penney's opinion testimony.

1. The Daubert Motion

Defendants move to exclude the testimony of Dr. Penney under Fed.R.Evid. 702, which provides:

Rule 702. Testimony by Experts

If scientific, technical, or other specialized knowledge will assist the trier of fact to understand the evidence or to determine a fact in issue, a witness qualified as an expert by knowledge, skill, experience, training, or education, may testify thereto in the form of an opinion or otherwise, if (1) the testimony is based upon sufficient facts or data, (2) the testimony is the product of reliable principles and methods, and (3) the witness has applied the principles and methods reliably to the facts of the case.

Defendants seek to exclude only that portion of Dr. Penney's testimony related to Timothy Heck's cause of death, namely that "Mr. Heck's death was likely primarily and directly related due (sic) to the toxic effects of carbon monoxide on his central nervous system." (Doc. # 82 Ex. 5 at 4; doc. # 68 at 1.) In support of the motion, Defendants argue (1) that Dr. Penney is not a medical doctor or forensic pathologist and therefore is not qualified to testify about cause of death, and (2) that Dr. Penney's methodology in arriving at his conclusion regarding the causation of Timothy Heck's death was not reliable.

i. Qualifications

A requirement of Rule 702 is that the witness be "qualified as an expert." The Rule, however, "contemplates a broad conception of expert qualifications." Hangarter v. Provident Life Accident Ins. Co., 373 F.3d 998, 1015 (9th Cir. 2004) (emphasis in original) (citations omitted). To satisfy this requirement only a " minimal foundation of knowledge, skill, and experience" is required. Id. at 1016 (emphasis in original).

Dr. Penney meets this standard with respect to his knowledge about the effects of carbon monoxide. Dr. Penney is a retired Professor of Physiology and former Adjunct Professor of Occupational and Environmental Health at Wayne State University in Detroit, Michigan, and currently is the Director of Surgical Research at Providence Hospital in Southfield, Michigan. (Doc. # 82 Ex. 2 at ¶ 3.) He has written more than 75 full-length scientific papers on the topic of carbon monoxide toxicology and exposure, at least 65 of which were subject to peer-review, and has published two books on the subject. ( Id. at ¶¶ 7, 11.) His opinions regarding carbon monoxide exposure and toxicology have been regularly relied upon by the Environmental Protection Agency, the World Health Organization, Centers for Disease Control and other renouned organizations. ( Id. at ¶ 10.) In short, Dr. Penney's "knowledge, skill, and experience" related to carbon monoxide and its effects are extensive.

Defendants nevertheless argue that Dr. Penney should not be permitted to testify as to the cause of Timothy Heck's death, given that Dr. Penney has no training in forensic pathology and is not a medical doctor. Generally, however, the precise title of an expert is far less important than the methodological rigor utilized by the expert in arriving at his or her conclusions. See Kumho Tire Co., Ltd. v. Carmichael, 526 U.S. 137, 152 (1999) ("[The trial judge's duty] is to make certain that an expert, whether basing testimony upon professional studies or personal experience, employs in the courtroom the same level of intellectual rigor that characterizes the practice of an expert in the relevant field.").

The court is mindful of Dr. Penney's lack of training specifically pertinent to the opinion he provides. Dr. Penney acknowledges that forensic pathologists have formal training in determining cause of death by postmortem examination and that he has no such training. (Doc. # 68 Ex. 8 at pt. 1, 55-58). Moreover, although Dr. Penney purports to have experience in the field, his testimony on this issue is contradictory, presumably because he is not legally qualified to perform forensic pathology. He testifies that he has never before performed a postmortem examination for purposes of forensic pathology. ( Id. at Ex. 8 at pt. 1, 56:19-22.) Yet he claims to have experience in looking at dead bodies and determining the cause of death, albeit solely in cases involving carbon monoxide. ( Id. at Ex. 8 at pt. 1, 58:5-18.) At the same time, he concedes that his conclusion regarding Timothy Heck is based on forensic pathology. ( Id. at Ex. 8 at pt. 2, 33:20-23.)

This objection does not go principally to Dr. Penney's qualification, but to whether Dr. Penney based his opinion regarding Timothy Heck's cause of death "on the types of scientific data" and "scientific techniques relied upon by medical experts." That subject is discussed below. His qualification, however, is minimally sufficient as to carbon monoxide poisoning.

ii. Reliability

Under Rule 702, "the trial judge must ensure that any and all scientific testimony or evidence admitted is not only relevant, but reliable." Claar v. Burlington N.R.R. Co., 29 F.3d 499, 501 (9th Cir. 1994) (emphasis in original); accord Daubert v. Merrell Dow Pharms., Inc., 509 U.S. 579, 589 (1993). To be reliable, "[p]roposed testimony must be supported by appropriate validation-i.e., `good grounds' based on what is known." United States v. Rincon, 28 F.3d 921, 924 (9th Cir. 1994) (citations omitted); see also Clausen v. M/V New Carissa, 339 F.3d 1049, 1056 (9th Cir. 2003) ("Scientific evidence is deemed reliable if the principles and methodology used by an expert are grounded in the methods of science."). The court therefore must "determine whether the analysis undergirding the expert's testimony falls within the range of accepted standards governing how scientists conduct their research and reach their conclusions." Daubert v. Merrell Dow Pharms., Inc., 43 F.3d 1311, 1317 (9th Cir. 1995) (" Daubert II"); see also Kumho Tire Co., Ltd. v. Carmichael, 526 U.S. 137, 153 (1999).

Here, the methodology purportedly utilized by Dr. Penney to arrive at his conclusion is valid. Dr. Penney claims to have performed a differential diagnosis, which entails making a list of all the likely or even possible causes of death, attempting to gather evidence for each of them, and then one by one crossing them off until the most likely cause is left. (Doc. # 68 Ex. 8 at pt. 2, 32:11-33:6.) Although Dr. Penney concedes that he did not actually draw up a list and instead performed the analysis "unconsciously or barely consciously" ( id. at Ex. 8 at pt. 2, 33:8-9), "federal courts . . . have recognized that a properly conducted differential diagnosis is admissible under Daubert." Clausen, 339 F.3d at 1057; see also Toguchi v. Chung, 391 F.3d 1051, 1060 (9th Cir. 2004); In re Berg Litigation, 293 F.3d 1127, 1130 (9th Cir. 2002).

Rule 702 additionally requires, however, that the witness have "applied the principles and methods reliably to the facts of the case." Although the focus is generally on an expert's methodology as opposed to his or her ultimate conclusion, Lust v. Merrell Dow Pharms., Inc., 89 F.3d 594, 598 (9th Cir. 1996), experts must show that they "arrived at their conclusions using scientific methods and procedures, and that those conclusions were not mere subjective beliefs or unsupported speculation." Claar, 29 F.3d at 502 (citations omitted). The burden of showing that the expert's methodology was properly applied to the facts rests with the proffering party. Lust, 89 F.3d at 598; see also Gen. Elec. Co. v. Joiner, 522 U.S. 136, 144 (1997); Domingo v. T.K.M.D., 289 F.3d 600, 607 (9th Cir. 2002). To carry its burden, the proffering party must show that each step of the expert's analysis in arriving at the conclusion was scientifically acceptable. See Joiner, 522 U.S. at 144; Schudel v. Gen. Elec. Co., 120 F.3d 991, 997 (9th Cir. 1997), abrogated on other grounds, Weisgram v. Marley Co., 528 U.S. 440 (2000).

Plaintiffs have not carried their burden of showing that Dr. Penney reliably performed his differential diagnosis to arrive at his conclusion. Dr. Penney provides, for example, no scientific explanation for ruling out the possibility that Timothy Heck was rendered unconscious and drowned from diving into the water and hitting his head on the bottom. The same is true of the possibility that Timothy Heck merely slipped and fell, hitting his head on the way to the water. This latter theory sits acutely in need of ruling out, given that according to Heck's brother, Heck had drunk eleven or twelve beers that day and one and one-half to two mixed drinks. (Doc. # 68 Ex. 3 at 48:11-14.) When asked how he ruled out such other potential causes of Heck's death, Dr. Penney simply responded that there was no evidence in the record to support a theory in which Heck was conscious when he received the blow to his head. ( Id. at Ex. 8 at pt. 1, 165:1-16.) Nobody had witnessed such a dive or fall. ( Id.) It appears that Dr. Penney used this rationale to rule out every theory of Heck's death in which carbon monoxide did not play a necessary, "but-for" causative role.

That the parties failed to gather or could not gather evidence directly supportive of a particular theory of causation (or in contrary thereto) does not constitute a sufficiently scientific reason for ruling it out. Where as here, an expert's opinion flows from a differential diagnosis, "[t]he expert must provide reasons for rejecting alternative hypotheses using scientific methods and procedures and the elimination of those hypotheses must be founded on more than subjective beliefs or unsupported speculation." Clausen, 339 F.3d at 1058 (citations and internal quotations omitted). In Clausen, for example, the court held that the plaintiff's expert had properly ruled out low salinity as the cause of massive oyster death that was the subject of the litigation. Id. at 1061. As scientific support for ruling out the low salinity theory, the expert relied on historic rainfall patterns showing that the oyster bed previously had been exposed to high rainfall which would lead to decreased salinity of the water without any associated oyster death. Id. He also pointed to the fact that the dying oysters did not exhibit any of the characteristics associated with anaerobic low-salinity death. Id. In debating the opposing expert, he suggested that the salinity testing arguably proving the opponent's causation theory was too infrequent to provide an accurate assessment of the salinity level during the relevant time period, explaining that saltwater concentrations change with the ebb and flow of tides and that oysters are able to endure long periods of low salinity by temporarily shutting down their filter-feeding processes. Id. at 1055. Finally, the record showed that every oyster in the area had been exposed to oil, which supported his theory of causation, as did his own histopathological examinations of several oysters in the area that had developed gill lesions in response to the contact with oil. Id. at 1054.

Unlike the expert in Clausen, Dr. Penney has provided no scientific explanation for ruling out any alternative possible causes of death. Instead, Dr. Penney focuses only on support for his own theory: for example, Dr. Penney testified that Timothy Heck's blood appeared more pinkish than normal blood in a photograph. (Doc. # 68 at Ex. 8 at 176:10-177:5.) However, Dr. Penney conceded that in the roughly 130 cases he had testified in, never had he relied on blood coloration to determine cause of death. ( Id. at Ex. 8 at pt. 1, 177:1-16.) In discussing the "reliable" indicators of carbon monoxide exposure, moreover, he did not even mention blood coloration. ( Id. at Ex. 8 at 157-161.) Dr. Penney's report similarly did not mention the colored blood. (Doc. # 82 Ex. 5.) The only slightly "reliable" indicator Dr. Penney alluded to in his deposition that was available here — the deceased's skin color — suggests that Timothy Heck had not been heavily exposed to carbon monoxide. (Doc. # 82 Ex. 5 at 4, ¶ 7.) Although some flexibility must be accorded Dr. Penney given that blood and tissue samples were unavailable, Dr. Penney's willingness to depart from his own articulated standards in drawing his conclusion is a cause for concern. Kumho Tires, 526 U.S. at 155-56 (noting that expert, in drawing his conclusions, had problematically ignored his own standards); Claar, 29 F.3d at 502 (noting that experts problematically had not made efforts to rule out possible alternative causes of the plaintiff's injuries despite their having admitted that this step was standard procedure).

Dr. Penney's report suggests, however, that he relied on other factors in coming to his conclusion. Timothy Heck was in the Channel on Labor Day, which is historically busy, and was near boats emitting carbon monoxide and being intermittently turned on and off. (Doc. # 82 Ex. 5 at 2; Doc. # 68 Ex. 8 at 158.) Timothy Heck had been exposed to heat and was drinking alcohol, moreover, both of which contribute to rendering unconscious a person exposed to carbon monoxide. (Doc. # 82 Ex. 5 at 4, ¶ 3.) Finally, Raymond Miranda, a friend of Heck, had experienced symptoms consistent with carbon monoxide exposure that day, and other drownings which occurred in the Channel over recent years involved carbon monoxide intoxication. ( Id. at Ex. 5 at 3, ¶¶ 7-8,13.)

Such circumstantial evidence, however, does not suggest that theories of causation independent of carbon monoxide intoxication are less plausible, particularly where many hundreds of other visitors to the Channel that day were similarly exposed without incident. "A differential diagnosis that fails to take serious account of other potential causes may be so lacking that it cannot provide a reliable basis for an opinion on causation." Clausen, 339 F.3d at 1058 (citations omitted). As noted by the Supreme Court, "[a] court may conclude that there is simply too great an analytical gap between the data and the opinion proffered." Joiner, 522 U.S. at 146 (citations omitted); see also Kumho Tire, 526 U.S. at 154. The methodology utilized by Dr. Penney here in reaching his conclusion has not been satisfactorily explained such that it would be repeatable by other scientists. As was the case in Daubert II,

[Dr. Penney] offers no tested or testable theory to explain how, from this limited information, he was able to eliminate all other potential causes of [death], nor does he explain how he alone can state as a fact that [carbon monoxide] caused plaintiff's [death]. . . . Indeed, no understandable scientific basis is stated.

"[S]cientific expert testimony carries special dangers to the fact-finding process because it can be both powerful and quite misleading because of the difficulty in evaluating it." Daubert II, 43 F.3d at 1321 n. 17 (citations and internal quotations omitted). In light of such dangers, Rule 702 requires the proffering party to demonstrate the verifiability of an opinion before it may be "cloaked with the mantle of an expert." Jinro Amer. Inc. v. Secure Invs., Inc., 266 F.3d 993, 1004 (9th Cir. 2001). Because Plaintiffs have not demonstrated the reliability of Dr. Penney's opinion testimony, the motion to exclude that testimony is granted.

2. Other Evidence of Causation

Despite the exclusion of Dr. Penney's opinion testimony, Plaintiffs have offered sufficient circumstantial evidence to create a triable issue as to whether carbon monoxide intoxication, potentially in connection with other factors, was a but-for cause of Timothy Heck's death. "In Arizona, as in most jurisdictions, an act or force need not be the sole cause of damage for causation to exist." Koory v. W. Cas. Sur. Co., 153 Ariz. 412, 414, 737 P.2d 388, 390 (1987) (citations omitted).

Arizona law holds that cause-in-fact exists if defendant's act helped cause the final result and if that result would not have happened without the defendant's act. Defendant's act need not have been a `large' or `abundant' cause of the final result; there is liability if the result would not have occurred but for defendant's conduct, even if that conduct contributed `only a little' to plaintiff's injuries.

The court's Daubert holding is not inconsistent with sending the circumstantial evidence to a jury. To testify as an expert and reap the benefits associated therewith, see Jinro America, 266 F.3d at 1004, the proffering party must explain the expert's methodology and its application to the facts. In this case, after choosing to perform a differential diagnosis, Dr. Penney failed to rule out alternative possible causes or to provide scientific explanation for not doing so. Dr. Penney's failure to explain his process would not necessarily preclude a jury from finding that carbon monoxide intoxication was at least one of the but-for causes of Timothy Heck's death. Moreover, to the extent Dr. Penney could have articulated a non-expert basis for finding other possible causes improbable, he would not be testifying about "specialized knowledge" that warrants expert opinion. Fed.R.Evid. 702. Finally, the City presented no challenge to Plaintiffs' circumstantial sufficiency of causation, and the County offered only scant discussion. The sufficiency of the actual trial evidence may be considered at trial.

C. Immunity

Defendants argue that statutory immunity bars Plaintiffs' claims involving Defendants' failure to pass ordinances addressing the carbon monoxide danger. Section 12-820.01, A.R.S., provides:

A. A public entity shall not be liable for acts and omissions of its employees constituting either of the following:

1. The exercise of a judicial or legislative function.

2. The exercise of an administrative function involving the determination of fundamental governmental policy.

B. The determination of a fundamental governmental policy involves the exercise of discretion and shall include, but is not limited to:

1. A determination of whether to seek or whether to provide the resources necessary for any of the following:

(a) The purchase of equipment.

(b) The construction or maintenance of facilities.

(c) The hiring of personnel.

(d) The provision of governmental services.

2. A determination of whether and how to spend existing resources, including those allocated for equipment, facilities and personnel. . . .

"It is well-settled law in Arizona that governmental immunity is the exception and liability is the rule." Alliedsignal, Inc. v. City of Phoenix, 182 F.3d 692, 694 (9th Cir. 1999) (citations omitted). The immunity statute is thus interpreted "with a view to finding immunity only if it clearly applies." Schabel v. Deer Valley Unified Sch. Dist., 186 Ariz. 161, 164, 920 P.2d 41, 44 (App. 1996). The court addresses both legislative function immunity and administrative function immunity under this statute.

1. Legislative Function Immunity

The legislative bodies of both the City and County decided to pursue various study and deliberation before deciding whether to enact carbon monoxide ordinances for the Channel. Timothy Heck's drowning happened before the City or County resolved whether to enact an ordinance limiting access to and idling in the Channel and while the City was considering and studying whether to do so. The City contends that its decision to study and deliberate was itself "exercise of a . . . legislative function," immunizing it from liability for deaths caused by carbon monoxide poisoning that could have been prevented by access limitations and idling controls such as the City's later ordinance provided.

On April 8, 2003, the City Council decided that "rushing to solutions" was not advisable and instead commissioned Sonoma Technologies to perform an initial empirical study. (Doc. # 86 Ex. 24 at 0004 (statements of Mayor Whalen and Council member Clark during meeting of City Council).) In May, the City Council met again and, instead of pushing through immediate changes in the law, decided to fund an informational campaign and commission further research by Sonoma Technologies. (Doc. # 70 Ex. 14 at 0010-0017.) The County Board of Supervisors, for its part, discussed the problem but decided to let the City take the lead. (Doc. # 67 Ex. 8 at 0090-0091; see also id. at Ex. 9 at 49.) The minutes from the meetings of both the City and County's legislative bodies show that these decisions involved whether to act now or after further information and study, with members offering divergent points of view on the question. (Doc. # 86 Ex. 24 at 0004; Doc. # 67 Ex. 8 at 0090.)

Section (A)(1) "provides immunity for the City's exercise of a legislative function," meaning it will cover only "an actual decision or affirmative act, not a failure to make a decision." Galati v. Lake Havasu City, 186 Ariz. 131, 134, 920 P.2d 11, 14 (App. 1996) (emphasis in original; citations and internal quotations omitted). However, a considered decision not to act is also immune under the statute. The statute immunizes both "acts and omissions," and, as held by the court in Goss v. City of Globe, 180 Ariz. 229, 232, 883 P.2d 466, 469 (App. 1994), an "omission" covered by the statute occurs when "in making its discretionary decision the public entity chooses not to do something." (Citations omitted). The focus of the inquiry is not whether the public entity did or did not pass an ordinance but whether the entity made a "considered decision, that is, one which consciously balances risks and advantages." Id. at 468, at 231 (citations and internal quotations omitted).

The difficulty with the City's analysis is that the decision to postpone decisionmaking, no matter how fully deliberated, is of a materially different kind than the decision of whether to enact an ordinance. Legislative immunity, as with administrative immunity, only protects decisions with respect to fundamental governmental policy. Goss, 180 Ariz. at 231, at 468 ("We do not believe that § 12-820.01 was meant to immunize a public entity from such non-decisions but only from actual decisions and the affirmative exercise of discretion with respect to fundamental governmental policy." (citations omitted)). The scheduling of when the legislature will make such a decision regarding fundamental governmental policy is not the kind of affirmative decision to act or not act protected under the statute. See id. (no immunity where City "effectively" decided not to make the allocation of funds for a guardrail), Galati, 186 Ariz. at 134, 920 P.2d at 14 (City's "prioritization of road construction projects" did not make failure to fund the project the same as a decision not to fund). Indeed, when it finished its study and deliberation, the City decided that such an ordinance was warranted. To read the statute as immunizing the decision to delay decisionmaking would stretch considerably the admittedly narrow scope and stated legislative purpose of the statute.

The City's claim of immunity also misunderstands the relation between A.R.S. § 12-820.01 and the underlying state common law. Nothing in A.R.S. § 12-820.01 exempts public entities from general tort duties, such as duties of possessors of land, merely because one way the duty may be discharged is by enactment and enforcement of a municipal ordinance. In enacting the immunity statutes, the Legislature stated its purposes: "[I]t is hereby declared to be the public policy of this state that public entities are liable for acts and omissions of employees in accordance with the statutes and common law of this state. All of the provisions of this act should be construed with a view to carry out the above legislative purpose." Ariz. Laws 1984, Ch. 285, § 1; see Fidelity Security Life Ins. Co. v. State Dep't of Insurance, 191 Ariz. 222, 224-5, 965 P.2d 580, 582-3 (1998). Therefore, assuming the City decided to possess and control Bridgewater Channel — which is in substance a road but for boats — the City took on the duty of a possessor to make safe. See Galati v. Lake Havasu City, 186 Ariz. 131, 134, 920 P.2d 11, 14 (App. 1996). Premises unsafe to an invitee must be made safe, or the danger adequately warned of so as to make safe. The City could not avoid its state law tort duties by "legislatively" deliberating over whether and how to fulfill those duties. The City may not rely on statutory immunity to avoid its state law obligations.

2. Exercise of an Administrative Function Involving the Determination of Fundamental Governmental Policy

If the decisions of the City to delay restraints on access and idling in the Channel are viewed as administrative in nature, they do not constitute the "determination of fundamental governmental policy" within the immunizing definition of § 12-820.01(A)(2) and (B). In determining whether § (A)(2) bars a claim, the key question is whether the government's action involved a determination of fundamental governmental policy. Fidelity Sec. Life Ins. v. State of Ariz., 191 Ariz. 222, 225, 954 P.2d 580, 583 (1998) ("[F]undamental governmental policy is the element which, first and foremost, must be present in the decision making process. Once that element is found to exist, the exercise of discretion, under the statute, may be presumed. The term `discretion' is used in the statute only to define an essential characteristic of determinations involving fundamental governmental policy."). The best way to describe a choice involving the determination of fundamental governmental policy is that it involves policy-making as opposed to policy-implementing. See Schabel v. Deer Valley Unified Sch. Dist., 186 Ariz. 161, 166, 920 P.2d 41, 46 (App. 1996) ("We discern that the immunity afforded to the kinds of decisions listed in subsection (B)(1) and (2) extends to determinations at a policy-making level rather than an operational level."); Galati v. Lake Havasu City, 186 Ariz. 131, 920 P.2d 11, (App. 1996) ("[We have] distinguished between discretionary governmental actions involving fundamental governmental policy, to which absolute immunity applies, and ministerial actions implementing that policy, to which immunity does not apply." (citations omitted)).

Here the fundamental governmental policy is that a possessor of land, including a municipality, must make it safe for invitees as against unreasonable dangers. The City is not free in its discretion to change or exempt itself from that fundamental policy. How the City carries out that fundamental policy which is beyond its control is largely an operational issue. See Schabel, 186 Ariz. at 166, 920 P.2d at 46 (distinguishing actions involving fundamental governmental policy from "operational level acts" which "concern routine, everyday matters, not requiring evaluation of broad policy factors; operational acts include kinds of road signs to place and what center line stripes to repaint" (citing Rogers v. State, 51 Haw. 293, 296-98, 459 P.2d 378, 281 (1969))); Galati, 186 Ariz. at 135, 920 P.2d at 15 (holding that while "the City is immune from a suit to force it to spend its resources," immunity did not bar the plaintiff's claim for operational-level negligence); Schabel, 186 Ariz. at 165-66, 920 P.2d at 45-46 (holding that statutory immunity did not bar claims for determinations made at the operational-level as contrasted to the policy-making level and that "[o]nce the district made a decision to have a playground at the school, it was obliged to implement its decision in a manner consistent with the duty of care owed to district pupils"); Goss, 180 Ariz. at 233, 883 P.2d at 470 ("The City also has a duty of repair and upkeep for which it does not enjoy immunity." (citations omitted)); Alliedsignal, 182 F.3d at 695 (noting that under Arizona law, a city is not generally entitled to immunity for negligence at the operational level).

Section 12-820.01 therefore does not immunize Defendants from Plaintiffs' claims.

IV. Conclusion

Plaintiffs have raised triable issues of fact as to whether the City owed Timothy Heck, as a public invitee, a duty to make safe the Channel. Although the opinion evidence of Dr. Penney as to cause of death is excluded, Dr. Penney may testify as to the effects of carbon monoxide, the significance of the discoloration of Heck's blood, and the possible effects of heat and alcohol when combined with carbon monoxide exposure.

IT IS THEREFORE ORDERED that Lake Havasu City's Motion to Exclude Testimony of Plaintiffs' Expert David Penney (doc. # 68) is granted, except as herein above stated. IT IS FURTHER ORDERED that Lake Havasu City's Motion for Summary Judgment (doc. # 69) is denied.

IT IS FURTHER ORDERED that Defendant Mohave County's Motion for Summary Judgment (doc. # 66) is granted.