Site information:

Site is 200 ft W of westbound lane, I-8 (P.M. 2.3), just N of Mountain Springs Rd, 2.3 mi E of county line, Mountain Springs. 

The OHP description above is vague, but I estimate the site would be somewhere around here:

32.674101, -116.108327

Nothing remains of the site, as far as I know.

Plaque information:

State plaque located near Desert Tower on In-Ko-Pah Park Rd

32.659217,-116.09967

Plaque text:

Mountain Springs Station Site

From 1862-70, Peter Larkin and Joe Stancliff used a stone house about a mile north of here as a store from which ox teams pulled wagons up a 30% grade. The San Diego and Fort Yuma Turnpike Co. used the site as a toll road station until 1876. The crumbling house was replaced in 1917 by another still visible to its east. But road changes, beginning in 1878 and culminating in today's highway, have left the older stone house ruins inaccessible.

First registered June 20, 1935. Plaque placed by the State Department of Parks and Recreation in, Imperial Valley Pioneer and Squibob Chapter, E Clampus Vitus. April 22, 1991.

Registered 6/20/1935