Colorado Plateau Karst
From Tobin and Weary (2004):
In northern and central Arizona, the Kaibab Limestone (Lower Permian) and its equivalents are karstic. North of the Grand Canyon, subterranean openings are primarily widely spaced fissured up to 1,000 ft (300 m) long and 250 ft (75 m) or more deep. South of the Grand Canyon, the fissures are more closely spaced and a few shallow caves are present. East of Flagstaff, there is an area of open fissures. These fissures are over 300 ft (90 m) deep, up to 1,000 ft (300 m) long, and up to 3ft (1 m) wide. They cut into the Coconino Sandstone, as well as the Kaibab Limestone (Colton, 1938).
There is a USGS scientist you can contact for more information about this aquifer.