Cal. Gov. Code § 23148
The boundaries of Solano County are as follows:
Beginning at the southwest corner, in San Pablo Bay, at the common corner of Contra Costa, Sonoma, Marin, and Solano; thence north, 261/2 degrees W., about six and one-quarter miles on the eastern line of Sonoma to the southwest corner of Napa at the mouth of the Huichica Creek; thence east, on the southern line of Napa, to the southeast corner thereof; thence north, on the line of Napa to the first standard north; thence east along said standard, on said Napa line, to the summit of Vaca Mountains; thence northerly, on said summit and Napa line, to Devil's Gate, on Putah Creek, which point forms the northwest corner of Solano and southwest corner of Yolo; thence easterly, on the line of Yolo, down said creek and the old bed thereof, to its intersection with the western line of R. 3 E., M. D. M., forming the northeast corner of Solano, with exterior angle in Yolo; thence south, along the line of Yolo, on said range line, two and seven-tenths miles, to the north line of T. 7 N., M. D. B.; thence east, nine and seventy-two one-hundredths chains, to the northeast corner of said township; thence south, to the first standard north, M. D. B.; thence east, on said standard line, to the center of Sutter slough; thence down said slough to Steamboat Slough, formerly called Merritt Slough, down said slough to the Sacramento River, down the Sacramento River about 13 miles to Suisun Bay; thence down the bay, along the center of the main ship-channel, in a westerly course about 18 miles, to the Straits of Carquinez; thence down the middle of said straits, and down San Pablo Bay, to the place of beginning; all these courses and lines being as shown by map and notes of William Wayne Fitch and E. H. Marshall, Surveyor and Deputy Surveyor of Solano County.
Ca. Gov. Code § 23148