I suspect a desert tortoise. I let others confirm ...there is a thread running on them now and there are similarities. Once confirmed you can read more so you can provide optimum care. Enjoy your new charge and ask questions as required.
Thread link.....https://tortoiseforum.org/threads/100-yr-old-desert-tortoise-yard-question.191986/
Gopherus agassizii, desert tortoise. The species is protected in its home state, and is the property of the state, with YOU now being the legal caregiver. It can't be sold, but there are turtle clubs that are authorized to take it if you ever decide you no longer want to care for it.