Cal. Gov. Code § 23157
The boundaries of Yolo County are as follows:
Beginning on the southeast corner, at the most easterly northeast corner of Solano, in Sutter Slough, at its intersection with the first standard north; thence west on said standard line to the west line of R. 3 E., M. D. M.; thence north on said range line to the northeast corner of T. 7 N., 2 E.; thence west nine and seventy-two one-hundredths chains to the southeast corner of T. 8, 2 E.; thence north on the easterly line of said township to the old bed of Putah Creek; thence westerly up the old bed and main Putah Creek to a point on the eastern line of Napa, in the canon, called Devil's Gate, where the highest ridge of mountains divides the waters of the Sacramento from Berryessa Valley, forming the most westerly of the southwest corner of Yolo and northwest corner of Solano; thence northerly along the highest ridge of said mountains to Cache Creek; thence east to the summit of the spur of the Coast Range which divides the waters flowing east into Bear Creek and Stony Creek, and those flowing west into the north fork of Cache Creek; thence along the dividing ridge, to the southwest corner of Colusa; thence easterly on southern line of Colusa to the Sacramento River, forming the northeast corner at the point of intersection of the southern line of T. 13 N., M. D. B.; thence down said river to Sutter Slough; thence down said slough to the place of beginning.
Ca. Gov. Code § 23157