Cal. Gov. Code § 23129
The boundaries of Nevada County are as follows:
Beginning at the northwest corner, at a point in the main Yuba River, at the mouth of Deer Creek; thence up the main Yuba to the mouth of the middle Yuba; thence up the latter to the mouth of the south fork thereof; thence up the south fork to the Bent monument situated at the falls of said south fork, in the NW. 1/4 of Sec. 10, T. 18 N., R. 13 E., M. D. B. & M., and being 1,000 feet, or thereabouts, southwest from the quarter-section corner between Secs. 3 and 10, township and range aforesaid; thence to the eastern line of the State, all on the southeastern and southern lines of Yuba and Sierra; then south, along the state line to the northeast corner of Placer; thence westerly, on the northern line of Placer to the source of Bear River; thence down Bear River, to a point south of the junction of Deer Creek and the main Yuba, forming the southwest corner; thence north, to the place of beginning.
Ca. Gov. Code § 23129