The Structure of the Pantano Beds in the Northern Tucson Basin

Abstract

A gravimetric survey has proved its usefulness in the Tucson Basin in locating important structural features, their geometric shapes and extensions. Interpretation was made possible through the correlation of available geologic and hydrologic data from water well logs and water table contour maps. Geophysical logs from a recently drilled test well in North Tucson have been interpreted and have confirmed the existence of another promising aquifer, namely, the deformed gravel which underlies the upper basin-fill aquifer. In most cases, it is apparently separated by a thin aquiclude of clay which results in artesian condition in the lower aquifer. Gravity interpretation discloses the presence of buried channels that may be of importance to groundwater exploration. The buried high basement ridges or faulted blocks as interpreted from gravity data add more information to the understanding of the hydrologic behavior of the basin. Deep drilling of test wells, such as the one drilled recently on Orange Grove Road, will be a useful check to the structures interpreted from gravity data. Geophysical logs of bore holes are of utmost importance in correlation of lithologic units and structures in addition to the hydrologic interpretation that is possible from these logs. The Pantano beds as described here are not promising for new groundwater sources that may be used for domestic needs due to the very low permeability and the expected poor quality of the water. Still more information is necessary to determine clear answers to many problems related to the geology and hydrology of this basin.