These ruins alongside the highway were once the mill site for the Golden Treasure Mine, about 5 miles away in the Black Mountains. The stone structure was an office building and the foundation of the actual mill can found a short distance away, both date to 1914. Today, the remains of the mill site are within Death Valley National Park and are thus protected by the national park service. Picnic tables and great views of the dry lakebed below make this a perfect spot to stop for lunch or just to stretch your legs.
If you go:
The short dirt road from CA Highway 178 to the site is easy to drive on and is fine for any vehicle. There is a restroom on site. Camping is not permitted near the ruins or in the valley below. The nearest gas or water is in Shoshone, about 30 miles away, so come prepared!
Links:

Badwater Road
Death Valley, California 92328 USA
Mailing address:
P.O. Box 579
Death Valley, California 92328 USA
Phone Numbers:
Death Valley Nat. Park Visitor Info
+1 (760) 786-3200
+1 (760) 786-3200