The date of the map might really be important toward determining the activity that occurred at this location. Here is some info from the Well Fargo website (history)
http://www.wellsfargohistory.com/faqs/ :
1852 ~
Wells Fargo & Co. founded by Henry Wells and William Fargo to provide banking and express services to Gold Rush California and the Pacific Coast.
1858 ~
Wells Fargo helps finance the nation’s first cross-country stagecoach line, the (Butterfield) Overland Mail Company, which carried mail and passengers from Missouri to California in 21 days.
1860 ~
The Pony Express shortens mail delivery between east and west to 10 days.
1863 ~
First National Bank of Philadelphia becomes the first national bank in the United States with Charter #1. (Later First Union, later Wachovia Bank.)
1866 ~
"Grand Consolidation": Wells Fargo acquires all major overland stagecoach firms in the West, connecting over 3,000 miles of western territory.
1869 ~
Transcontinental railroad and telegraph completed.
1872 ~
Northwestern National Bank (later Norwest) is founded in Minneapolis, by investors including William G. Fargo.
1875 ~
Wells Fargo drops comma from name (“Tale of the Comma”).
1879 ~
Wachovia National Bank opens in Winston, North Carolina.
1888 ~
Wells Fargo’s "Ocean to Ocean" express service moves commercial business across the country in four days.
Employee handbook states: “Proper respect must be shown to all—let them be men, women, children, rich or poor, white or black.”
1906 ~
San Francisco earthquake and fire. Wells Fargo provides horses and wagons to evacuate residents and deliver supplies.
1918 ~
Federal government takes over nation’s express business—including Wells Fargo—as a wartime measure. Wells Fargo Bank continues.
If I had to venture a guess, I say it was a stage stop acquired after 1866 and it no doubt would have been used to 'express' gold, mail, and other items to and from that site. As I said, just a guess. Since there are 'shafts', was the site in a big mining area (as shown on later topos) ?