[aerohead]

Continental crust has an average geothermal gradient of 55-F per mile ( 20-C/km ).
According to Halliburton Oil Well Cementing Company, average continental crustal thermal gradients will produce:
110-F @ 2,000-FT
140-F @ 4,000-FT
170-F @ 6,000-FT
200-F @ 8,000-FT
230-F @ 10,000-FT
260-F @ 12,000-FT
290-F @ 14,000-FT

In California, the USDOE had a geothermal well in Long Valley, at 6,000-10,000 feet, near a dormant volcano.
At 20,000-feet, it is 1200-C ( 2160-F ).
Northern California geothermal takes advantage of near-surface volcanism as well.
Carson City, Nevada has active geothermal electric power generation. It's a caldera for a super-volcano, like Yellowstone, Wyoming.
Seems like, unless there's magma nearby, a 'typical' hole in the ground cannot provide 'commercial' levels of ambient heat for the necessary super-heated steam.