The type of pick you have there, can very well date to the 1880's. I've seen this same style of cast steel pick, often found in context with 1870's-1880's mining activity. By the mid-1860's, most of the picks were manufactured in quantity, and cast complete, ready to use once a stout handle was affixed. The earlier picks more often seen in 1840's-1850's context, were comprised of two separate halves, either forged or sometimes cast, and then hot hammer welded together.
The cache you seek may potentially be in the area, as these finds are supported by the time period of activity you are researching.
CC Hunter