Cal. Gov. Code § 23101
The boundaries of Alameda County are as follows:
Beginning at the southwest corner, being the common corner of San Mateo, Santa Clara, and Alameda; thence easterly along the northerly boundary of Santa Clara to the corner common to Santa Clara, San Joaquin, Stanislaus and Alameda; thence northwesterly and northerly along the boundary line between Alameda and San Joaquin, as described in the field notes of the survey of said line, as adopted by the Board of Supervisors of Alameda County, California, on February 6, 1869, to the corner common to Alameda, Contra Costa and San Joaquin; thence in a general westerly direction along the boundary line between Alameda and Contra Costa, as described in the field notes of the survey of said boundary line, filed November 19, 1877, in the office of the Clerk of Alameda County, to the intersection thereof with the generally most southern line of Parcel 1(R/W) of exhibit "B" of the FINAL ORDER OF CONDEMNATION to Contra Costa County Water District, an agency of the State of California, as recorded December 3, 1993, under Series No. 93425262 Official Records Alameda County, California; said intersection point being northeasterly 12,512 feet, more or less, from County Boundary Monument 89-1, as shown on "Joint Boundary Retracement Survey Alameda and Contra Costa Counties Monument Map, Exhibit 3," dated February 1962 and filed under Alameda County file no. 64-A-29-1; thence southerly, westerly, and northwesterly along said most southern line to the reintersection with the aforementioned boundary line between Alameda and Contra Costa, said reintersection point being northeasterly 10,353 feet, more or less, from County Boundary Monument 89-1; thence westerly along said boundary line between Alameda and Contra Costa to its intersection thereof with the northeastern line of a 12-foot path, said intersection being on the corporate limits of the City of Oakland as said limits were established by Ordinance No. 1132, changing said limits, adopted May 14, 1991, by the city council of said city; thence northerly and northwesterly along said northeastern line and corporate limits from a tangent which bears north 28°43'22" east, on a curve to the left having a radius of 71 feet and arc length of 85.47 feet to a point of compound curvature; thence from a tangent which bears north 40°25' west, on a curve to the left having a radius of 306 feet and arc length of 121.06 feet to a point where said northeastern line, being also said corporate limits, intersects the northern line of Villanova Drive, 50 feet wide; thence continuing northwesterly along said northern line, being also said corporate limits, from a tangent which bears north 7°48'59" west, on a curve to the left having a radius of 200 feet and arc length 241.06 feet; thence north 76°52'30" west 133.94 feet; thence tangent to the last mentioned course, on a curve to the right having a radius of 175 feet and arc length of 131.97 feet to a point of reverse curvature; thence from a tangent which bears north 33°40' west on a curve to the left having a radius of 200 feet and arc length of 151.33 feet to the intersection of said northern line, being also said corporate limits, with the corporate limits of the City of Oakland, being also the common boundary of Alameda and Contra Costa Counties, as same existed prior to Ordinance No. 1132; thence continuing westerly along said boundary line between Alameda and Contra Costa to the most westerly point where said line is coincident with the line dividing the Rancho San Pablo from the Rancho San Antonio; Thence westerly along the northerly boundary line of the Rancho San Antonio to the initial point of the description thereof, as recorded in Liber "B" of patents, page 30, records of Alameda County; thence southwesterly in a direct line to a point in San Francisco Bay, said point being four and one-half statute miles due southeast of the northwest point of Golden Rock (also known as Red Rock); thence southeasterly in a direct line to a point from which the lighthouse on the most southerly point of Yerba Buena Island bears south 72 degrees W., 4,700 feet; thence southeasterly in a direct line to a point on the southerly line of T. 2 S., R. 4 W., M. D. B. & M., distant thereon two statute miles west of the southeast corner of said township, forming the corner common to San Francisco, San Mateo and Alameda; thence southeasterly along the eastern line of San Mateo to the place of beginning.
Ca. Gov. Code § 23101