Sounds fishy to me. Those old coins were made mostly around San Francisco. You say the Mormons' wagon upset near Redding as they were migrating to Calif (from Utah I suppose), so how did they acquire those coins before they arrived? BTW those old coins didn't have numismatic value until the 20th Century, so I doubt a banker or anybody else would pay a premium for it.
If Clear Creek is as muddy as you say, those gold coins are on bedrock beneath the mud. How deep is the mud? If the creek changed course over the past 150 years (they do, ya know) those coins could be a hundred yards away from the current bed.
If yer still determined to try out yer metal detector, search the river bank for a cutbank or dugway. The old trail makers cut out the river or stream bank with shovels to allow their wagons easy entry/exit. Although the old trail no longer exists spotting the cutbanks on both sides of the creek can pinpoint where the old crossing was.
If you find em, let me know and I'll send you my address. Happy huntin.