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.
Resources - Coal
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.