Dude, where's my horse?: Lost horse mine
Lost Horse Mine is one of the more challenging trails at Joshua Tree, but is definitely worth the effort. The origin story of the mine does involve a lost horse. A man by the name of "Dutch Frank" had the original claim to the site that became Lost Horse mine. Johnny Lang happened upon the site when he was trying to track down some of his lost horses. Long story short, Frank ended up selling the claim to Johnny. (For the longer version: https://www.nps.gov/jotr/learn/historyculture/lhmine.htm) The mine operated intermittently between 1893 and 1936 and produced more than 10,000 oz of gold and 16,000 oz of silver (625 and 1,000 lbs)...that's a lot of precious metal. A large portion of the mine is still intact today, however there is a fence around it so you can't right next to the mine but you can get pretty close. This is not your typical mine with a shaft carved into a mountainside and little rail cars. It's actually a stamp mill that was connected to the veins of gold and silver ore and used a complex system of gears and levers to stamp the metal into a more compact form. (This is my super non-technical definition...)
Lost Horse Mine trail also offers some great views of the desert and mountains. You can go out and back or take the slightly longer loop option, which I think is worth the extra mileage. You can also see the remains of an old house...maybe where the miners lived?...not sure. All that's left is a bed frame and a chimney.