Once the second largest town in San Joaquin County, Mokelumne
City was established in 1850. When hydraulic gold mining was at its
height, a flood wiped out Mokelumne City. The survivors resettled
farther from the river in a community they called New Hope. The
railroad later renamed New Hope to Thornton in gratitude to a local
rancher who gave them free right of way.
Go to the listed coordinates. Then, starting from the edge of
the northern concrete piling of the trestle at water level nearest
the center of the bridge, go to a point 81 yards up river near the
opposite bank at a bearing of 80 degrees (relative to true
north).
A GPS unit is not the only way to measure distance in the field
nor is it always the best. I recommend using a laser range finder
to measure the yardage if you have one. That's how I measured it.
(Google Earth agrees with my distance measurement. But Google Earth
is less portable than a laser range finder and its imagery is often
about 10 feet off.)
Or you can just go out there and look for it. This cache is not
very hard to see from your boat--except during times of high flow,
which is when I think it will be nearly impossible to find.