Cal. Gov. Code § 23131
The boundaries of Placer County are as follows:
Beginning at a point where the west line of T. 10 N., R. 5 E., M. D. B. & M., intersects the northern line of Sacramento; thence north on range line to the northwest corner of Sec. 6, in T. 10 N., R. 5 E.; thence east on the township line to the southwest corner of Sec. 31, T. 11 N., R. 5 E.; thence north on the range line to the northwest corner of T. 12 N., R. 5 E.; thence east to the southwest corner of Sec. 34, T. 13 N., R 5 E.; thence north to Bear River; thence on the southern line of Yuba and Nevada, up said river to its source; thence east in a direct line to the eastern line of State of California, forming the northeast corner; thence southerly along said line to the northeast corner of El Dorado; thence westerly, on the northern lines of El Dorado and Sacramento to the place of beginning.
Ca. Gov. Code § 23131