Steep and then somewhat sandy travel - not ideal for a run.
This out-and-back trail leaves from the Desert Loop Road at marker #9, dropping into a fairly steep side canyon with a few switchbacks. After descending to the canyon floor after a little under one mile, Upper Rattlesnake Canyon
heads to the right (north) up the wash.
To stay on this trail, continue to the left (south) through and above the wash. After a half mile or so (around mile 1.5 from the beginning), look for the remains of an old homestead from the 1930s.
The trail continues south to the mouth of the canyon and the boundary of the park without connecting to any other trails. The southern reaches of the trail can be explored based on time, water/food, and energy.