During the middle of the day on Saturday, I went for a quick spin on Trail 100. Weather was not half bad - high 70s.
Trail 100 has a lot of nice easy trails, with decent views for being in the middle of a sprawling city.

On a clear day, this would be a nice shot of downtown Phoenix:

Not too far in, and I’m just over a mile outside of the 7th and Thunderbird trailhead - I had just finished a quick climb, and was a bit higher than street level and the parking lot. I clip in my right foot like usual, and start rolling. I put my left foot down - didn’t clip. I try again - didn’t clip again. A third time, and my foot gives way.
My left crank arm popped clean off, as if it had unscrewed.

Since I had just finished a climb and had a long, gradual downhill in front of me, the only near-logical thing to do was to clip the right foot back in and coast on down to the trailhead.

This is the first time I had rode with one leg - and with the clipless pedals, I could still pedal along. Until the right half started to slip out a little bit… so maybe not the brightest move.
Anyways, I made it back to the trailhead in one piece. It ended up being a really short ride, just under 6 miles. But it was fun nonetheless.
I didn’t have any tools with me, so I drove my bike over to DNA Cycles for a quick fix. The guys there had it done in a few minutes and they took care of my chain and Reba.