If you have lost something or found something, please contact your teams coach. He/She can check with the coach of the other team to see if they, or one of the families on their team, happened to pick it up.
If it was left at Castle Rock there's a chance it is in the Snack Shack. At the other fields you may want to check with the schools to see if it made it's way to their lost and found.
Walnut Creek Little League does not have an official centralized lost and found.