RE: I found a frog in the desert

Years ago, my parents found a turtle in their backyard. We also live in high desert here in Colorado, and their house is nowhere near water.
I think there are some species of turtle naturally in the state, but based on what species he was and where he was, they guessed he had been someone's pet that was abandoned or lost. When they didn't find a human looking for a turtle, my aunt adopted him.
I wonder if this guy might have been a pet too?