Urgent: What type of snake is this?

[Person]

Hello!

I found this snake in a fish tank at a park, no idea what it is though. I think it may be a garter snake, but it is not lined so IDK. It doesn't try to bite or slither away too much, pretty docile actually, so I'm thinking it isn't wild? The fish tank was all cracked, but it had a snake dome house so it might be a pet. Not sure though.

Should I keep it or let it go? IDK if its wild or not, but it seems pretty nice. I've had a ball python before so I know how to figure out what it needs, just need to know what it is first.

We're in Utah and live where there are a lot of houses (not near the mountains or any lake, just houses).