Legally, in most jurisdictions, you report it.

Ethically, if there no ID or any identifiable infomation nearby, its very unlikely for the owner to be found, I think it’s fine to keep it. (If there is an ID, you should give it to the authorities.)

If it were any amount above $1000, I wouldn’t touch it, it could be drug money, don’t want to get caught up in some drug cartel bussiness.

Keep it mind, cops could pocket it. So if you really want to find the owner, you should probably try to find them yourself, at the cost of your time and potentially getting falsely accused of being a thief.

TLDR:

Options:

1. Pocket it
2. Give it to the authorities
3. Find the owner on your own time
4. Leave it where you found it

Your choice.