State of Arizona Bureau of Geology and Mineral Technology Geologic Investigation Series Map GI-2-D LANDFORMS 112"00' TEMPE QUADRANGLE, MARICOPA COUNTY, ARIZONA ".,.' ( Phoenix "'~"~ Cathy S. Wellendorf James T. Bales Troy L. Pewe • I-0:"""::'~'~-To PllfI Pedlm.,t I I --- . Tampe Department of Geology Arizona State University SUP'Ontitution ~ MI.:; 1986 -" Prepared in cooperation with the cities of o '0 M ilas I , Tempe, Scottsdale, and Phoenix, and the Arizona State Land Department INTRODUCTORY STATEMENT 3 6.'5/ III S W (PARADfS£ 000 FE ET 11 1 · 52'30 " 33"30' The Tempe Quadrangle is in the Sonoran Desert Section of the Basin and Range Physiographic Province. The alternating basins and ranges were produced during a period of block faulting which occurrod in M id -Tertiary time, approximataly 12 to 17 million years ago. The re la tive ly upthrown blocks form the ranges, while the downdropped blocks fonn the ba sins. Ero­ sion of the bedrock hig hlands of thesa ranges has contributed great thicknesses of dabris. forming alluvial fans at the base of the highlands. As t he ba sins f ill with alluvium, the dis ta l ends of these alluvial fan s cOli lesce Into a nea rly flat, elCtanslva basin floor. Many small. isolated knobs of bed rock. such as T~ mp e Butte, Bell Butte, 1md Twin Buttes, represent the tops of hills and ranges that are tieing buried by the infi lling allUVium. z Mountains in arid regions are commonly bordered by a realitively Smooth, eroded bedrock o surface called a pediment. A break In slope separates the broad , concavtl upward pedimont Sut­ face from the steep mo untain f ront. The Papago Pa rk Pediment is a partly buried, gullied ped i­ ment. The Original upland mass has be!!n reduced to a number of isolated, residual bedrock hills called inselbergs. The Papago P3rk Pediment is small. only 7.5 mi 09.5 km l. II is thought to 1M! about 3 to 5 million years old. This age is Uased on the rclm lvely extensive development of caliche In tha colluvium which overlies the pediment. As the surrounding basins filled with alluvium, the debris could no longer btl transpocted away f rom tha pediment, and accumulated on the bedrock surfaces, ~here it became cemented by caliche. As thEl bordering Salt River has lowered Its base level. streams d raining tha pediment have cut into this calichified colluvium, locally aJlPosing bedrock in the floors and sides of the gullies. ST The pediment Is distinguished from an alluvial fa n: a pediment is a surface of erosion, bu t an alluvial fan is a sur1ace of deposition. Ailuvia l f ans are not well devaloped w ithin this quadrangle due to the absence of large mountnins. The rlistal portions of alluvial fans from surrounding moun­ tain ranges converge to fonn the contlnOUS surface of the basin f loor. Dry washes draining the "'" fans of Camelback Mountllin and the McDowell Mounteins are tributari es to Indian Bend W ash, a shifting, ephemeral straa m which is a tributary to the Salt Rivar. The Salt River has contributed to the basin-fill deposits by trllnspottin~ al luvium from the Superstition-Goldfield-MazetZ91 Mountains In the east. As me river locelly mea nders across the valley, It MS Oroded laterally forming an eJltensiva floodplain. Four paired alluvial terraces bordar the modern chanr18l, and represent older floodplain levels. These floodpill in remnants were left behind as the river cut down through alluv ium which It had deposited at an eerller time. Three ter­ rar.:o levels can be distinguished w ithin the TerTlle Quadrangle. Each terrace reflects a period of downcutting due to uplift of the mountains in the east, which causes a rejuvenation of the ri ver. The terraces converge nsar Tempe, where the older terraces disappear undel the basin floor . '31 Tho Iowost terrace, the Leh i, is only 5 It (1.6 m) above Ihe dry river bed near Tempe, and rises to 18 ft 16 m) above the ri ve r 24 miles (40 km) upstream. A higher terrace, the Bl ue Point. is not recognized In I hls Quad rangle. The most prominent tartllce is the Mesa. on which most of the T 2 N. citios of Mesa and Tempe are built. II is 10 to 15 ft (3 to 4.5 m) above the dry ri ver bed atTemJle. 21B ft (67 m) above the river at StllWClrt Mountain Dam. an d mora than 290 ft (90 m) above t ho river near Roosevelt Dam. The highest and oldest terrace, t he Sawik. is the most fragmentary. It is :>'" about 45 ft (15 m) above the dry river bed at Scottsdale and the Sa lt River IMlan Reservetion. whore It h..'lS boon buried under all uvia l fan deposits horn Camelback: Mountain and the McDowell Mounta ins. Although the river has shifted back and forth across the va lley, and its level is now lower. the groin-size distribution, the roundne5S. and the ~pheric i ty of the cob ble ~ indicate that conditions under which the older gravels were dep06ited are very simila r to the modarn condilions of deposition. Comparison of the rock types of terrace daposlts with those of the modern channel show that the source has 1'1 01 changed th roughout the hist ory of the Salt River. The downstrnam convergence of the l erraces suggests a continual reg ional uplift of the mountains to the east and T.! N. north, w ith the relative subsidence of tho basin. The older Mesa and Saw ik Terrace deposits show various stages of caliche development, and could be up to 2 million yea rs old. Similar terraces on the Gila River downstream nee r Arl­ 27',," 1- 27'30 " ington are covered by lava flows 2 to 3 million yoars old. , , . , On November 4, ,9n, Nwl! (unpublished data) found II fossil tortoise (l<!to Pleistocene 7) at a depth of 6 It 12 m) under overbank silt on the Lohi Tarnu:e 1/ 4 mile t1016 ml sou theast of Lehi, Arizona 12 1/2 miles 14.2 kmJ east of Tempe Quadrangle). Teeth of II Pleistoc8f1e horse were found in the Lehl Terrace deposit ellst of Sky Herbor Airpon, south of Washington Stroet, north of the Salt RIver INalions and Lindsoy, 1976) . The tOElt h were identrfied to be from Equus ucciden(iJfk> nnd their condition suggests the specimefls had not been transported with t he rivar gravels nor reworked f rom older deposits Presence of those teeth supports a late Pleistocene age (Rancho­ labrean Land Mammal Age) for the Lehi Terrace deoosit. As the river abandons a former level, the terrace gradually becomes covered by en­ croaching allUVium from t he surroundillQ highlands. This alluvIal blanket Is thicker to the aast, where the mountains are higher end closur to Ihe river. South Mountains is clooe enough to the river to have caused partial buria l of even the youngest terrace. Different landforms are the resuh of different geologic conditions . Parameters used to dif­ ferentiatolondforms include topogralllljc expression, sloplt, calic he development, drainage and in­ cision. Identification of a particular l<!n dform allows a prediction of the reilltive flood hazard, the penneability, t he 1nIaiiabie materi.'ll resources, and t~ excavation conditions. 18 ." ,I .I' SELECTED REFERENCES 30gB Christenson, G. C., and P6we, T. L . 1978, Environmental geology of the McDowell Mountain area, Maricopa County, Arizona - Landform s map: Arizona Bu rea u of Geology and Min­ era i Technology. Geologic Investigation Series, GI-l -B, 1:24,000. 25' Cordy. G. E.. Holway, J . V., end Pew~, T. L. , 19n, Environmental geology of the Pnradisc V;:lIley bfc=,;, Quadrangle, Maricopa County, Arizona: Tempe. Arizona, unpublished folio of maps pl e­ pa red for the City of Scottsdale. 14 plates. 1 :24,000. Den ny. C. S .. 1967. Fans and pediments: American Journal of Science, p. 81-105 Kokalis, P. G., 1971 , Terraces of the lower Salt River Valley . A rizona' unpubli shed Master of Science thesis. Arizono Stllte Un iversity, 103 p . Lee , W. T., 1905. Underground waters 01 Salt River Va lley : United States Geo logical SUf\lr!y Water Supply and Irrigation Paper 1'10. 136,196 P Nations, J . D., and Lindsay, E. , 1976, Pleistocene Equus from SaH River terrace gravels. PhoeniX, Arizona: Joornal of A rizona Academy of Science, volume 11, p . 27-28. Pewe. T. L , 1978. TerracllS of the lower Salt River Valley in rela tion to Ihe Late Ctlilezoil: history ol l he Phoenix Basin, Arizona: in a iln, D. M., and Nwe. T. L., Guidebook to the geology of central Arizona: Arizona Bureau of Geology and Minerai Techno logy, Spm:ial Paper number 2, p. 1-45. Pope, C. W ., 1974, Geology 01 the lower Vcrdr: Rive r Valley, Maricopa County, Arizona: I .~B unpublished Ma~ter of Science I hesl~ , Arizona State University, 104 p. •. i This map involves a general evaluation on a broad scale and does not preclude · - I ~I t he necessity of site investigation. L ,. 870 FEET SYMBOLS * Vertebrate fossil locality :> 55' '15 11 1 °52'30 " BASE MAP FROM U.S. GEOLOGICAL SURVEY TOPOGRAPH IC MAP. 1:24.000 SERIES * TE M PE QUADRANGLE (1952 PHOTOFI EV ISED 19B7 ) Additional revisions compiled by the Geological 6CO.) 7003 FEET Survey from aorial photographs taksn 1978 and otha. sources. This information not f ield chocked. M a~ edited 1982. 1) 1M GRID ANO 1982 MAGNETIC NOlrnH OEC LINATION AT CENi EA OF SH EET EXPLANATION Active geologic fluodlliam af Ilia Sa il River - Undulatory topograph\l of Sawlk Terrac e - High alluvial terrace remnant of the Sail River.