This depression in the trees marks the location of a 710 foot deep sealed shaft, the most northerly mine entry in the Mt Diablo Coal Field.
The Independant Shaft was sunk in 1865. By 1867 the company had failed and the shaft became inactive except as a means of pumping water from the nearby Eureka Mine. It was opened again in a 1900 by the Pittsburg Mining Company but closed after less than a year. It is now completely sealed and all that remains are a small array of vertical iron spikes on which teh hoist works were mounted.