The Rio Tinto Borax company operates one of the largest open pit mines in the world. This mine is the richest deposit of borate, which is used in hundreds of consumer products. This visitor center is really, really cool. Interesting exhibits, knowledgeable docents and also home to the only remaining 20-mule team wagons. These wagons were used to haul borate ore from Death Valley to the railroad. The mine was originally a underground mine and you can still see the original shafts. It's a working mine and so one can watch the giant ore trucks zipping up the steep grades.
If you go:
Open seven days a week from 9:00 a.m. to 5:00 p.m., excluding major holidays and weather permitting. RV Parking and stunning view of the pit mine from the roof of the museum.
Links:

Suckwo Road
Boron, California 93516 USA
visitor.center@borax.com
Mailing address:
14486 Borax Road
Boron, CA 93516-2000 USA
Phone Numbers:
Visitor Center Information
(760) 762-7925
(760) 762-7925