I am back to report for future reference that the local Wells Fargo bank branch will only convert currency, no coins, and only for customers as they deposit the proceeds in an account so that if the currency proves to be counterfeit they can charge it back to the customer. So in other words an account is required.
As I have no accounts at Wells Fargo I drove on quite a few miles to a Bank of America branch where I do have an account. They have exactly the same policy.
Each one of these banks will deposit the converted amount and allow immediate withdrawal of the full amount.
I now have about 30 dollars in GBP and Euro coins with which I can do nothing at present. Quite a bother. I must say I wish everyone would just use USD. It would be so much easier.