California Code, Government Code - GOV § 23146

The boundaries of Sierra County are as follows:

Beginning at the south corner of Plumas, in the center of Slate Creek;  thence easterly on the southern line of Plumas to the range line between T. 21 N., R. 13 E., and T. 21 N., R. 14 E., M.D.B. & M.;  thence north on said range line, to the northwest corner of T. 21 N., R. 14 E., M.D.B. & M.;  thence east on the line between T. 21 and 22 N., M.D.B., to the state line forming the northeast corner;  thence south on said state line to the northeast corner of Nevada, a point east of the Bent Monument;  thence west to the Bent Monument;  thence down the south fork of the middle Yuba River and down the middle Yuba River to a point 10 miles above the mouth of the latter;  thence in a straight line northerly to a point on the north fork of the Yuba River known as Cuteye Foster's Bar;  down said river to the mouth of Big Canon Creek, then up said creek four miles;  thence in a straight line to the point of beginning.