In the foreground of this photo, at The Box rock climbing area near Socorro, is a basalt lava flow that has a brown varnish. A fresh piece of the rock is shown on the smaller photo below, with a penny for scale. This is the basalt of Broken Tank, which flowed into the area from the south about 8.5 million years ago. This lava has interested Richard Chamberlin, who mapped it out, and myself for many years because one can use it to infer paleo-slopes and paleo-geography at this time period.
But recently I found out another intriguing fact about this basalt: a piece of this same outcrop is now on Mars!