It's not terribly apparent in this photo, but there's a fracture zone/fault running along the ceiling, roughly in the middle of the shot. It's clear that this structure was the one the miners were following initially. The target, I was told by another visitor to this area many years ago, was deposits of "blue-white" clay, which could be rinsed to give tiny amounts of gold dust and wire. The clay deposits were (and in small amounts, still can) found in open spaces within the fractured areas. It must have been terribly demanding and dull work. Knowing what I do about practices during the 1890's, when this area was first worked (there was another, smaller surge during the early 1930's, if I remember correctly), and knowing that there was no good power source, they must have hand drilled holes for dynamite blasting. This would involved repeatedly pounding a long steel drill, with a sledge hammer, into this incredibly tough rock. It would've been back-breaking labor, with no real promise of a payoff. I suspect at this mine, the payoff must have been pretty marginal- there's probably 300 to 400 feet of tunnel. So they found enough gold to encourage them to dig more, but not enough to persuade them to continue beyond a certain point.