Thanks, Arizona. The actual details aren't that dramatic. When I walked back a few paces on the otherwise-normal dirt path, I noticed that there was a 2-inch tree root that ran parallel to the path about 3 inches above the dirt. It was embedded in the side of the trail, and about the same color as the dirt. The only thing I can come up with is that my boot landed on the root and slid off, toward my other foot, and threw me off balance.

The damage wasn't too bad, and I never lost consciousness. However, I do think the 80+ temperature, 80+ humidity, and the fatigue they created probably combined to make me less alert than I normally am. I also think it allowed me to make a rookie mistake.

I rested for a while in a shaded clearing, deciding whether to hike out or continue. When I decided to hike out, I realized that I didn't need to carry the extra 2 quarts of water I had picked up to take to camp. So, I took a couple of healthy swigs from the container and dumped the rest. That's when I realized that the water was in my dirty-water reservoir, and hadn't been filtered yet. I was using a 1-quart "clean" bottle and 2-quart "dirty" bottle with a Hydroblu (Sawyer clone) filter, so there was no way to filter all 3 quarts. Despite different color caps and the size difference (which should be obvious tip-offs about which bottle is which, I missed the visual clues. Again, fatigue can really cloud your brain.