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;11 14 ? p The consolidated formations younger than the Mancos contain water generally adequate only for domestic and stock supplies, although in sor~ areas where these young~r rocks are thick, supplies largo enough for small towns ml.ght be obtained. Hare information is needed, however, before the water-yielding properties of the younger rocks, especially those of Tertiary age, can be appraised properly, even in general terms. For an understanding of the areal extent of the various water-bearing formations in western Colorado, the reader is referred to the geologic map of colorado.lI certain general I J , I j,f Burbank, W.S., Lovering, '1'.8., Goddard, ~-n., 1935, Geologic map of colorado: Survey. E.N., and Ecltel, U.S. Geological statements, however, may be useful to those who do not have ready reference to the geologic map. In the western one-fourth of the State, rocks older than i;ha Mancos predominate at or near the surface south of the Grand Valley; whereas, rocks younger than the Mancos predominate at or near the surface north of the Grand Valley. Between the western one-fourth of the State llIJ1d the Front Range of the Bocky Mountains, the complex geologic structure has exposed rocks of all ages, the occurrence of anyone formation or group of formations within a particular age group being relatively small in areal extent. Again using the Hancos as a reference, most of this area has surface rocks older than the Mancos or is covered with igneous rocks of Tertiary age underlain by rocks l'IlUch older than the Mancos. None of these are knol'm to be good aquifers except locally. scattered throughout the aren, however, are small areas under- lain by water-bearing beds ranging in age from Triassic to Tertiary. The water-bearing properties of these units probably are similar to those of corresponding units in tho area to the west. Ground wster is known to occur in some of the dense rocks of sedimentary, metamorphic, or igneous origin where fracturing, faulting, welltllering and solution have created extensive cracks, crevices and solution channels that lie below the water table. Detailed studies commonly are necessary to determine the extent of such areas, and few such studies have been made in Colorado.