Um...

 On Monday, I looked outside and saw this. Hello? Where did he/she come from?

 I put him/her into a cardboard box. It enjoyed some lettuce...

(Not pee, spilled water...)

Amazing...they really are like little dinosaurs with shells.

I put a notice on NextDoor, but no one responded, so we took the tortoise to the Humane Society the next morning. Be well, little stranger!