Cal. Gov. Code § 23112
The boundaries of Humboldt County are as follows:
Commencing at the point where the north line of T. 12 N., R. 1 E., H. B. & M., intersects with the Pacific Ocean; thence east on said township line to the northeast corner of T. 12 N., R. 3 E., H. B. & M.; thence south to the southeast corner of said T. 12 N., R. 3 E., H. B. & M.; thence east on the north boundary line of T. 11 N., R. 4 E., 11 N., 5 E., and 11 N., 6 E., H. B. & M., to the Klamath River; thence following said Klamath River in a southerly direction to the mouth of the Salmon River; thence in a southerly direction, following the ridge of the mountain that divides the waters of the Salmon and its tributaries from the waters of the Klamath and Trinity Rivers, and their tributaries to the northern line of Trinity; thence southwesterly on the line of the mountain, being the northern line of Trinity, to a point in the Trinity River directly east of the mouth of Mad River; thence southeasterly, up Trinity River, to the mouth of its south fork; thence southeasterly, along the eastern side of said south fork, 100 feet above high water mark, to the mouth of Grouse Creek; thence south, to a point on the fortieth degree of north latitude, being on the northern line of Mendocino, and forming the southeast corner of Humboldt; thence west on said line, to the Pacific Ocean; thence northerly, along the ocean shore to the place of beginning.
Ca. Gov. Code § 23112