Most of the major thermal areas of Yellowstone are related to the ring
fracture zones of the Yellowstone caldera (fig. 22). Many deep-seated
faults and fractures in these zones are presumably situated above the
main source of heat of the thermal system. Thus, they provide convenient
avenues of travel for underground waters to circulate to great depths,
there to become heated and then rise to the earth’s surface (fig. 45). A
few areas like Mammoth Hot Springs and Norris Geyser Basin, on the other
hand, are not within the ring fracture zones of the caldera. In these
areas, the thermal activity is commonly related to other prominent zones
of faulting which also afford readymade channelways for the circulation
of hot water and steam.