Down in the southern reaches of Joshua Tree National Park are Porcupine Wash and the Ruby Lee Millsite.
The Park Service says the mill dates back to the 1870s. They probably know something I don't. I could only find evidence that the mill site dates from the Depression Era of the 1930s, when many people were out in the desert looking for gold and trying to make a living. Ruby Lee Rule claimed the mine and mill in March 1936. By 1948, it was owned by A. Dietemann. Production from the mine is unknown, but it is unlikely it was very much.
The mine itself is four miles off to the west from the mill site and much deeper into the hills. It consists of a minor series of shallow shafts and prospects.
I noticed the letters “M.W. 1933” carved into a granite boulder along the old road to the mill site. I’m unsure what “M.W.” stands for or who made this historic inscription; it is another backcountry mystery.