Introduction 4 Location of study area 4 Geologic setting 4 Acknowledgments 6 Part 1. Geological investigations 8 Data sources 8 Stratigraphy of the basin fill 8 Nogales Formation (lower basin fill) 9 Distribution 9 Age and contacts 9 General appearance and thickness 10 Clast composition 10 Depositional environment 11 Upper basin fill 11 Structure 12 Subbasins 12 Structural control of the upper Santa Cruz River 13 Upper Santa Cruz River gradient and Quaternary faulting 13 Summary 16 Part 2. Geophysical investigations 17 Data compilation 17 Separation of the basin gravity anomaly 17 Basin fill density functions 18 Drillhole information 24 Estimation of depth to bedrock 32 Estimation of thickness of upper basin fill 36 Summary 37 References 39
Introduction 3 Acknowledgments 6 Stratigraphy of the Exxon (32)-l well 6 Methods and data used 6 Stratigraphic nomenclature 7 Basin-fill units 7 Fort Lowell Formation 8 Tinaja beds 12 Upper basin-fill deposits 12 Unsampled interval 13 Stratigraphic Unit A 13 Stratigraphic Unit B 15 Lower basin-fill deposits 16 Stratigraphic Unit C 16 Stratigraphic Unit D 17 Pantano Formation 18 Conglomerate, muds tone, and andesite flow 19 Rock-avalanche deposit 20 Middle Tertiary volcanic and sedimentary rocks 23 Lamprophyre(?) dike 23 Intermediate-composition lava flow 23 Conglomerate 23 Silicic tuff 24
highs and lows. No evidence was found to support the presence of a proposed buried bedrock high on the west side of the Palominas structural subbasin near Nicksville. Evaluation of well data indicates the bedrock high is an artifact of several mislocated wells on the draft structure contour map prepared by the Arizona Department of Water Resources. Well-numbering1 system in Arizona.
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