Cal. Government Code § 23150

The boundaries of Stanislaus County are as follows: Beginning at the common corner of Stanislaus, Santa Clara, Alameda, and San Joaquin, on the summit of Mount Boardman, of the Mount Diablo Range, as shown on the survey and map of Wallace and Stakes, May, 1868; thence southeasterly, on the summit line of that range, being the eastern line of Santa Clara, to the northwest corner of Merced, forming the southwest corner of Stanislaus, as established by the survey and map of A. J. Stakes, July, 1868; thence northeasterly, on the line as established by that survey, to the junction of the Merced and San Joaquin Rivers; thence down the San Joaquin seven miles; thence in a direct line a little north of east to a monument established by the survey of A. J. Stakes, being on the summit of the ridge between Merced and Stanislaus, and marking the common corner of Tuolumne, Merced, Mariposa, and Stanislaus; thence northwesterly, in a direct line, and crossing the Stanislaus River, to the monument established by the survey and map of George E. Drew, May, 1860, on the north bank of the Stanislaus River; thence northwesterly, on the line of that survey, to its intersection with the western line of R. 10 E., M. D. M., which point is marked by a monument establishing the north corner of Stanislaus County; then south, on that range line, to the Stanislaus River; thence down the latter to its mouth in the San Joaquin River; thence southwesterly on the line as surveyed and mapped by Wallace and Stakes, May, 1868, to the place of beginning.