We can, but only in specific areas. Iceland has a unique geology that affords them this power source.
The areas most viable for geothermal power are in the Great Basin (ie, northern NV, southern ID, northeast CA, etc), perhaps northwest WY.
Everywhere else, it would require some real work to develop the resource.
http://geoheat.oit.edu/dusys.htm
A type of Geothermal can also be used in places where there are no volcanoes or hot springs to use for heat:
IIRC, there's a new-ish geothermal plant near Reno that's producing power. A few years back I was somewhat involved with a pilot geothermal plant in southern Idaho but they were having many problems with corrosion and mineral deposits in the plumbing.
Believe me, it isn't as easy as just tapping into the hot water and letting it do its thing. Geothermal water is loaded with all sorts of goodies: gold, silver, copper and many other minerals, some quite nasty. They can really plug up the "works" in elaborate heat-exchange equipment. They're the source of many ore deposits, like the famous Comstock Lode. In the U.S. geothermal energy remains one of those vague unproven "alternative" energy sources that the enviros claim will replace oil quickly -- not!