Our mysterious mystery seed from last week was indeed an acorn, as many of you guessed. It was probably from a live oak, possibly from the coast live oak, Quercus agrifolia, although that isn't sure.
Clues that it might be an acorn included the discolored area on the left side. It seemed like it might have had a cap originally, like acorns have.
There aren't too many species of oaks with long, narrow acorns, mainly the live oaks.
Are coast live oaks even found in Arizona? Well, there is one at The University of Arizona Arboretum in Tucson. I have to admit the acorns look a bit darker red in the photographs on that site. I did read that the acorns can be variable.
What do you think about the photograph at this art site. Look similar?
What do you think?