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The structural geology of the Foy Ridge area, Twin Buttes, Arizona Item Type text; Thesis-Reproduction (electronic); maps Authors Burroughs, Richard L. Publisher The University of Arizona. Rights Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author. Download date 09/10/2021 10:14:24 Link to Item http://hdl.handle.net/10150/553929 THE STRUCTURAL GEOLOGY OF THE FOY RIDGE AREA, TWIN BUTTES, ARIZONA by Richard L. Burroughs A Thesis Submitted to the Faculty of the DEPARTMENT OF GEOLOGY In Partial Fulfillment of the Requirements For the Degree of MASTER OF SCIENCE In the Graduate College UNIVERSITY OF ARIZONA » 1 9 5 9 £ cn cu I 9 f ? / % STATEMENT BY AUTHOR This thesis has been submitted in partial fulfillment of re­ quirements for an advanced degree at the University of Arizona and is deposited in the University Library to be made available to borrowers under rules of the Library. Brief quotations from this thesis are allowable without special permission, provided that accurate acknowledgment of source is made. Requests for permission for extended quotation from or reproduction of this manuscript in whole or in part may be granted by the head of the major department or the Dean of the Graduate College when in their judg­ ment the proposed use of the material is in the interests of scholar­ ship. In all other instances, however, permission must be obtained from the author. SIGNED: 6/ APPROVAL BY THESIS DIRECTOR This thesis has been approved on the date shown below: 7%t/. E. B. MMo Date Professor or Geology CONTENTS TEXT Page Abstract.......................... ............................ v Acknowledgments.................................. vii Introduction............................ ....................... x Stratigraphy............. 1 General.......... ........................ 1 Cambrian rocks........................... 2 Bolsa quartzite.......................... 2 Abrigo formation...... .................................. 4 Devonian rocks.......................................... 12 Martin limestone.... ...................... ............ 12 Mississippian rocks......... ............................... 20 Escabrosa limestone................... 20 Pennsylvanian-Permian rocks.......... .................. 26 Introduction......... 26 Horquilla formation............... 27 Andrada formation.......................... 30 Schemer (?) and Concha formations....... ............... 31 Quaternary rocks and sediments....... ................ 37 Pleistocene (?) and/or Recent rocks and sediments........ 37 Igneous rocks............................. 39 Structure........ 42 Introduction. ........ .................................••• 42 Structural control of topography...................... 43 Dip of beds and character of folding....................... 44 Northwest plunging anticline.......... 48 Minor folds.............. 49 Foy Ridge and Foy Ridge fault........ ...................... 52 Southwest side of Foy Ridge..... ......................... 53 Normal faulting (?)............. ...................... .. 56 Thrusts northwest of Foy Ridge.......... ................. 60 Reverse fault at northwest end of Foy Ridge......... ....... 61 Concha thrust.......... 63 Dike-Sill and stock...... ................................. 63 Relationship to near-by areas.............................. 67 Geologic history...................... 69 References cited......... 75 iii ILLUSTRATIONS Page Plate 1. Index map................ ................. viii Plate 2. Panoramic view of Foy Ridge................. ix Plate 3. Fig. 1. Joints in Bolsa quartzite.................. 6 Fig. 2. Thrust zone in Bolsa quartzite...... 6 Plate 4. Fig. 1. Banding of Abrigo limestone.... ........... 11 Fig. 2. Banding of Abrigo limestone........ 11 Plate 5. Fig. 1. Folding in the Abrigo formation............ 23 Fig. 2. Typical topographic surface of the Escabrosa limestone.... ...... 23 Plate 6. Fig. 1. Typical brecciate Permian Concha limestone......................... 35 Fig. 2. Typical brecciate Permian Concha limestone............ 35 Plate 7. Fig. 1. Thrust fault in Abrigo fold................ 47 Fig. 2. Tight fold in Martin limestone............. 47 Plate 8. Fig. 1. Aerial view of minor folds in Devonian Martin limestone........................ 51 Fig. 2. Detail of minor folds in Devonian Martin limestone......... 51 Plate 9. Fig. 1. Aerial view of Bolsa Overthrust............ 58 Fig. 2. Aerial view of Bolsa Overthrust...... 58 Plate 10. Fig. 1. Bolsa quartzite thrust over Concha formation............. 65 Fig. 2. Bedding in Pleistocene (?) or Recent sediments.................. 65 Plate 11. Geologic map of the Foy Ridge area......... ........ Pocket Plate 12. Cross sections Fig. 1. A-A*... .... Pocket Fig. 2. B-Bt-Btt............................... Pocket Plate 13. Cross sections Fig. 1. C-Ct-C"............................... Pocket Fig. 2. D-D’........... Pocket Plate 14. Topographic map of the Twin Buttes quadrangle....... Pocket Plate 15. Diagrammatic cross-sections illustrating development of Foy Ridge structure Figs. 1, 2, 3 and 4 .............................. Pocket iv ABSTRACT Foy Ridge is located about twenty-six miles south-southwest of Tucson, Arizona, and about a mile north of the Twin Buttes mining dis­ trict. The sediments of the Foy Ridge area range in age from Cambrian to Recent. Separation of the Paleozoic section into mappable units has been complicated by post-Permian metamorphism. This metamorphism has destroyed any fossils that were probably once present, although a few remains of a Devonian Cladopora reef have been recognized. The metamorphism has caused a recrystallization of the limestones and an alteration of the shales to homfels with stringers of epidote. The result is a sequence of altered Paleozoic rocks closely resembling one another. Lateral compression acting in a northeast-southwest direction played the major role in the tectonic history of the Foy Ridge area. Foy Ridge is the inverted limb of a large fold overturned to the north­ east. As the fold was being produced thrust faults and wrench faults formed in the limbs. These first faults were cut off by the Foy Ridge fault that formed in the southwest limb of a northwest plunging anti­ cline. This anticline was thrust forward (southwest) and upward until it was pressed against the inverted limb (Foy Ridge) of the adjacent fold. A disharmonic fold probably formed in the normal limb of the v major fold of which Fay Ridge is a part. Thrust faults in this dis- harmonic fold repeated the lower Paleozoic section on the southwest side of Foy Ridge. As compression continued the last major thrust of the area was produced. This was the Bolsa Overthrust, which probably originated in the core of the disharmonic fold. It cut across the in­ verted limb of the major fold and may have also cut across the crest of the northwest plunging anticline northeast of the Foy Ridge fault. Intrusive activity followed or accompanied the overthrusting and folding of the area. This was closely followed by post-intrusion normal faulting. The Twin Buttes, two prominent hills immediately east of the thesis area, are a southeastern extension of the northeastern limb of the northwest plunging anticline that formed the hanging wall of the Foy Ridge fault. The "breached anticline" of the Twin Buttes mining district is probably related to the normal limb of the fold that formed Foy Ridge. The synclinal area between these two folds is covered by alluvium. vi ACKNOWLEDGMENTS The author is indebted to Prof. Evans B. Mayo of the University of Arizona who has supervised and directed this thesis problem. In the field, the author profited from the visits of Prof. Mayo, Prof. Willard C. Lacy, and graduate students from the University of Arizona. Thanks are extended to Dr. Donald Bryant for identification of the fossil Cladopora and to the Department of Geology of the University of Arizona for the use of the aerial photographs which greatly facili­ tated the field work. The writer wishes to express his gratitude to Mr. and Mrs. Frank D. Kozak for reading the stratigraphic portion of the manuscript and for their many helpful suggestions. Thanks are also extended to the many people who participated in discussions and who offered constructive criticism on the interpretation of the geology of the thesis area. The cooperation given by the residents of the area is greatly appreciated. vii RIVER ---- - .WINSLOW ------ O HOLBROOK COLOR ADO COLORADO ^ GLOBE FLORENCE O q WINKELMAN BENSON O TWIN BUTTES TOMBSTONE bisbee i NOGALES ° Q DOUGLAS I MILES Plate l. - Location map, Foy Ridge area, Twin Buttes, Arizona AFTER CUMMINGS 8 ROMSLO (1950) e Panoramic view of Foy Ridge looking west from West Twin Butte* Sierrita Mountains in background. Plate 2 INTRODUCTION In south central Arizona is located the arid Santa Cruz Valley. On its western border, southwest of Tucson, are the Sierrita Mountains which have shed a thin veneer of Recent sediments over the eastward sloping pediment. Within this debris-covered area, several small hills project through the outwash, offering samples of the geological prob­ lems beneath. One of these hills, known as Foy Ridge, is the subject of this thesis. Foy Ridge is located about twenty-six miles south-southwest of Tucson, Arizona, and about a mile north of the Twin Buttes mining dis­ trict (PI.

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