>>I'm not happy about the releasing of a non-native,

Me either! That's how we acquired our sulcata. Our sulcata was in terrible shape with her horrendous pyramids & then was shot so I know that she was thrown away by a jerk but this tortoise you found looks fabulous.
That makes me wonder if this is an escaped pet & if someone is looking for it. You might try looking at the lost & found ads in your local newspaper & look around the neighborhood to see if you find any lost tortoise posters on poles & such. One other thing, I know not many people do this but we did.. we microchipped our tortoise. It wouldn't hurt to have this one scanned just to be sure.
Otherwise.. good luck with your new beautiful pet!
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PHRatz