Site information:

General Patton Memorial Museum, just off the 10 on Chiriaco Summit, 28 mi E of Indio

I'm not sure Camp Young was actually located at the site of the current museum or not.  Nothing remains of the site, as far as I know.

33.661681,-115.722529

Plaque information:

State plaque and private plaque

State plaque text:

Desert Training Center, California-Arizona Maneuver Area

The D.T.C. was established by Major General George S. Patton, Jr., in response to a need to train American combat troops for battle in North Africa during World War II. The camp, which began operation in 1942, covered 18,000 square miles. It was the largest military training ground ever to exist. Over one million men were trained at the eleven sub-camps (seven in California).

Plaque placed by the State Department of Parks and Recreation in cooperation with the General Patton Memorial Museum and the Bureau of Land Management, November 11, 1989.

Private plaque text:

The Desert Training Center
Camp Young

Maj. Gen. George S. Patton Jr., U.S. Army, selected Camp Young as headquarters site for the Desert Training Center in March 1942. Camp Young was the administrative center for a simulated theater of operations that would eventually extend from Pomona, CA to Phoenix AZ, from Yuma, AZ, to Boulder City, NV, and would include a network of training facilities at Camps Clipper, Coxcomb, Granite, Ibis, Iron Mountain and Pilot Knob in California, and Camps Bouse, Horn, Hyder and Laguna in Arizona. Between 1942 and 1944, over one million men trained on the surrounding desert and participated in the most realistic war games under the harshest conditions imaginable. In a very important sense, many battles of World War II were won on these desert lands during those maneuvers.

This memorial is dedicated to the soldiers of the U.S. Army who participated in these events. The spirit which they displayed generated a spark that spread into every oversees theater in which they served.