Geology and Ground- Water Resources of The Los Alamos Area New Mexico By ROY L. GRIGGS With a section on QUALITY OF WATER By JOHN D. HEM GEOLOGICAL SURVEY WATER-SUPPLY PAPER 1753 Prepared in cooperation with the Atomic Energy Commission UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1964 UNITED STATES DEPARTMENT OF THE INTERIOR STEWART L. UDALL, Secretary GEOLOGICAL SURVEY Thomas B. Nolan, Director The U.S. Geological Survey Library catalog card for this publication appears after page 107. For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C. 20402 CONTENTS Page Abstract.____--_______-_-__-__________-__-___-__--__--_--------_ 1 Introduction._________-_-__---___-_____---_---_-_-_-_-_--__-__---_ 2 Purpose and scope._______________-_--__-_______---_-_--__-_--_ 2 Acknowledgments---------------------------------------------- 4 Location-numbering system.-___________________________________ 4 Geography __-___________-_-__-___-_-____--__--_-___-___-----_---__ 6 Location and accessibility-_________--_---__--_---_-_-_-_____--- 6 Physiography ________-___-_____-____--_-___-___--__-_-_----_-- 8 Regional setting-__________'_____________-__________-__-_-__ 8 Los Alamos area_ ___.____________-___-_____---_-_-_-__--__ 8 Topography and drainage__________________________________ 15 Climate and vegetation___________________________________ 15 Geology.______________________^. _______-_-_-_--__-_-_-_-_-_--_--__ 16 Stratigraphy._-________-____________--___-___-_--______-_-___- 16 Rocks of the Rio Grande depression. ________________________ 20 Santa Fe Group----.---.-----.------------------------ 20 Undifferentiated unit_____________________________ 20 Puye Conglomerate.-._____________________________ 28 Basaltic rocks of Chino Mesa_______________________ 37 Old alluvium_________-_-__________-__-___-_--__-_-__ 41 Volcanic rocks of the Jemez Mountains volcanic pile__--__-____ 42 Tschicoma Formation.__________-_-___-_--____--_______ 42 Latite and quartz latite unit._______________________ 43 Pyroxene andesite unit.____________________________ 44 Tewa Group._________________________________________ 45 Bandelier Tuff_____________________-___-_____.____ 46 Cerro Toledo Rhyolite__ ___________________________ 56 Cerro Rubio Quartz Latite____-_____-____-_-________ 57 Valles Rhyolite________-________.__---_-__-____._ 58 Caldera fill. ______________________________________________ 59 Alluvium. ________________________________________________ 72 Valles Caldera area-__---___-----_--_--_-___-----_-_-_- 72 Rio Grande area__-_---___--__-_______--______-_-_-__ 73 Structure. _ ___________________________________________________ 73 General structure__________________________________________ 73 Faults -------__-_-_---_________-__-_-_--__-_--___-_--_ 73 Valles Caldera_______.____________________________________ 74 Geologic history_______________________________________________ 74 Water resources___________________________________________________ 79 Surface water in the Valles Caldera area_____--_-______-_--__---_- 79 Ground water in the Valles Caldera area _________________________ 80 Valle Toledo------__--___________-____-____--____-_--_--_- 80 Valle Grande_______________________________.______________ 81 in IV CONTENTS Water resources Continued Ground water in the Valles Caldera area Continued Recharge, movement, and discharge-_----___________________ 82 Aquifer hydraulic coefficients______________________________ 84 Effect of wells on ground-water regimen ______________________ 84 Chemical quality of water, by John D. Hem__________________ 85 Valle Toledo-_______________-__---___________-_____.__ 85 Valle Grande-______-__-_----_-------------------_____. 87 Relation to use______________________________________ 87 Surface water in the Rio Grande area_-_---_-_-----_-_-_-________ 89 Guaje Canyon___--_-_-____________---_-_________-____.--_ 90 Los Alamos Canyon. ______________________________________ 90 Pajarito Canyon_________________________________________ 90 Canon de Valle--------_-------------------------_-_---_-_- 91 Water Canyon.___________________________________________ 91 Ground water in the Rio Grande area______--_____-__--__________ 91 Tschicoma Formation._____________________________________ 91 Bandelier Tuff__ ____________________---_----___-_________. 92 Puye Conglomerate._______________________________________ 92 Basaltic rocks of Chino Mesa._______-_-----_-____-_________ 93 Undifferentiated unit of the Santa Fe Group._________________ 94 Occurrence of water____________________________________ 94 Recharge, movement, and discharge _____________________ 94 Aquifer hydraulic coefficients..__--___---___________-__ 95 Pumping tests_____-_____________-_____________________ 96 Water-level changes caused by pumping__________________ 99 Chemical quality of water. _____________________________ 100 Summary of ground-water resources. __ __________________________ 101 Valles Caldera area___________________________ _____________ 101 Rio Grande area--____-_________-___-_---_---_-_-__-______- 102 References_ _____________________________________________________ 103 Index.___________________________________________________________ 105 ILLUSTRATIONS Page PLATE 1. Geologic map of the Los Alamos area.-________________ In pocket FIGURE 1. System of numbering wells and locations._________________ 5 2. Map of north-central New Mexico showing location of Los Alamos area.________________________________________ 7 3. Map of topographic features in Jemez Mountains region.____ 9 4. View looking eastward to Sangre de Cristo Mountains._____ 10 5. Generalized geologic map of Jemez Mountains region ______ 11 6. View looking westward to Jemez Mountains.______________ 13 7. View looking northward across the Valles Caldera__________ 14 8. Chart showing generalized stratigraphic relations...________ 18 9. Graphic logs of wells in Guaje Canyon ____________________ 22 10. Crossbedded sandstone of the Santa Fe Group.____________ 24 11. Horizontally bedded siltstone of the Santa Fe Group-....-.- 25 12. Fanglomerate member of the Puye Conglomerate in Guaje Canyon _____________________________________________ 32 CONTENTS V Page FIGUBE 13. Fanglomerate member of the Puye Conglomerate in upper part of Guaje Canyon_____________________________________ 36 14. Lump pumice of Guaje Member of the Bandelier TufL_____ 49 15. Bandelier Tuff, Pueblo Canyon_-______________________ 50 16. Otowi and Tshirege Members of the Bandelier Tuff showing disconf ormity_ _______________________________________ 53 17. Generalized schematic diagram along axis of San Antonio Creek_________________________________ 60 18. Generalized schematic diagram across axis of San Antonio Creek_______________________________________________ 61 19. Generalized schematic diagram of Valle Grande____________ 62 20. Sketch plan of Guaje Canyon well field._________________ 97 TABLES Page TABLE 1. Selected logs of wells and test holes in the Los Alamos area__ 63 2. Records of wells and test holes in the Los Alamos area______ 70 3. Records of selected springs in the Los Alamos area__---____ 86 4. Chemical analyses of water from the Los Alamos area______ 88 GEOLOGY AND GROUND-WATER RESOURCES OF THE LOS ALAMOS AREA, NEW MEXICO By EOT L. GRIGGS ABSTRACT The Los Alamos area is in north-central New Mexico, approximately 60 miles north-northeast of Albuquerque and 25 miles northwest of Santa Fe. The town of Los Alamos is near the center of the area. Tbe area, for the most part, lies on the eastern flank of the Jemez Mountains volcanic pile that rests on and rises above tbe zone of faults at the western margin of the Rio Grande depression. Tbe western edge of the area is near the center of the Jemez Mountains volcanic pile, and from here it extends eastward across a segment of tbe interior mass of flows and onto an outlying apron of tuff that lies on sedimentary and volcanic rocks belonging to the western part of tbe Rio Grande depression. Both the volcanic and the sedimentary rocks are of Late Tertiary and Quaternary age. The volcanic rocks of the Jemez Mountains pile comprise the Tscbicoma Formation, Bandelier Tuff, Cerro Toledo Rhyolite, Cerro Rubio Quartz Latite, and Valles Rhyolite. The Tschicoma Formation includes the older interior mass of flows of the volcanic pile, which, within the area, can be divided into two mappable units: (1) latite and quartz latite (older), and (2) pyroxene andesite (younger). The Bandelier Tuff forms the outlying apron of. tuff and consists of three members which are, in ascending order, the Guaje, Otowi, and Tsbirege Members. Tbe Cerro Toledo Rhyolite, the Cerro Rubio Quartz Latite, and tbe Valles Rhyolite form volcanic domes within and ad­ jacent to the Valles Caldera, a part of tbe collapsed interior of the volcanic pile. A body of sedimentary deposits occurs in the Valles Caldera. Tbe suite of rocks of the Rio Grande depression is included in the Santa Fe Group. Tbis group is represented in tbe area by three mapped formations. Tbe stratigraphically lowest formation, called in tbis report tbe undifferentiated unit of tbe Santa Fe Group, is a sequence of arkosic sand and silt and some included basalt. Above the undifferentiated unit is the Puye Conglomerate composed chiefly of latitic debris derived from tbe interior mass of the Jemez Mountains volcanic pile; tbe Puye also includes some interbedded basalt and a lentil of arkosic conglomerate. The arkosic conglomerate at the base of the formation is the Totavi Lentil of tbe Puye Conglomerate, and tbe overlying