Hi,
I checked to see if your sandbox database for SierraCountyEvents was synced to the live database and it looks like the live database needs to be synced. This might be the reason why the 404 is showing up. Follow the information here to sync your sandbox database to the live site and publish the site one more time to be sure all the bases are covered.
I tested it out on completely different site and that should resolve the 404 issue.
Best Regards,
Edward