Thorns!

It shouldn't be very surprising, but every so often I'm reminded desert plants have nasty thorns!

Two thorns in the foot. I only felt one.

First one went in at an angle that didn't reach my foot.

The second one got me! 

These were from a mesquite tree.  Back in the day, goodness, already 23 years ago, I had a sturdy work boot I also hiked in. Heavy but strong and with a thin layer of metal to prevent thorns (or probably nails) from penetrating the sole.  Seemed to hold up better than these boots, but then it was well over double the going rate for your average work boot.  Now the $100 hiking boots are low end, but that's all the City will reimburse us in a given year for boots.