However the area was first developed as a coal mining area. The coal was used to power steam locomotives and the rail way. The mine opened and closed several times. Most recently is was called the Tesla Mine, after a developer for electrical energy and alternating currents. During that period the coal was sent to Stockton to power the factories there. At one time it was proposed to make a coal powered generator there, but this was not done as it was felt it couldn't compete with hydroelectric power.
Also in the area was a pottery works. There was also sand and clay manufacturing. The sand was sent to Stockton for manufacturing into glass.
Today it is hard to recognize the original mine locations. Entry into the area is discouraged for fear of falling into a mine shaft. The links below provide additional historical information as well as a mad of the canyon.