Mastadon Mine Loop Trail in Joshua Tree National Park starts at either Cottonwood campground or Cottonwood Spring on the Lost Palms Oasis Trail. After 0.25 miles turn onto Mastadon Mine Loop Trail to reach the mine. Continue on the trail to reconnect with Lost Palms Oasis Trail.
It's 4.7 miles loop from Cottonwood campground or 4.45 miles from Cottonwood Visitor Center.