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 (lWashington 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

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. Gently slop­ Co ll uvia l slopes - Accumulations of debri S on st eep slopes and the base of alterna ting bars and channels with rel ief of approxim ately 15 ft (4.6 m). slop­ ing W to 2%), sli ghtly undulating surface of low relief. Locally burie d by t hl~ isolnted bedrock highlands. Surfaces nea rly flat with slopes generall\l ex­ Ing eest to west (2 t o 5%). No caliche development. Boundary Is scarp of distal ends of alluvial fan s f rom McDowell Mountains. Th iS all uvial bla nket. eeading 16%. Caliche strong ly dElvelopod. Well drained, flooding slight . Lehi Terrace. Flooding is common Ifl years of eJl treme rain fall. Floodplain together with erOSion, has hlurred distinct ion of the scarp ber.veen this and cepable of containing a flow of approximately 150,000 cubic feet per second. the younger Mesa Terrace, leaving only a gt!ntle brea k in rehel . The terrace This floodplain docs nol .:orlSidf!J ilttificial channels. obst ructiorno, and deposits arc tight ly cemented by caliche. regulatory devices. (See Flooding 1G1-2-EI lor delineation of floodplain Pediment - Low, eroded bedrock surfaces with slopes generally less than according to regulated and unregulated flows of various frequencies. 10 % (except steep, isolated bedrock knobs called inselbergs w hich rise above the pediment surface!. Topography is und ulating, channels incised up to 25 ft (7.1 m) deep. Ca liche strongly developed in the overlyiog colluv ium. Basin f loor - Nearly level to very gently sloping (0 to 2% ), nearly center of Drainage well developed, floo ding generally contained in incised d mrmels. basin at the distal ends of all uv ial fans. Individual fans no longer dlscemable, Hashed pattern indicat es where colluviu m and weathered bedrock have been Floodplain 01 Indian Bend W as h - Nearly level floodplain 10 t02% slopel ex­ but coa lesce to fo rm a basin-fill deposit. Land surfaces generally flat Wi th dry artlflcally re moved for commercial use . tending north to south ac ross the basi n f loor, ioining the Salt Rive r Bound­ w ashes incised less than 5ft (1.5 m), and relief between washes less tt1an 3 ft BP - BUried pediment, tted rock: surface covered by strongly cal!chified aries dellnealll the 100 yeilr floodplilin. Ind liln Bend Wash is in cised less than ( 1 m). BFL coll UV ial-alluvial debris. 2 to 50 f t (0.5 to 15 m) thi ck. Bedrock loca lly exposed 20 ft 16.1 m). Caliche strong ly developed except w here floodplain crosses BFL - Thin (less t han 15 ft 14.6 mIl blallket of South Mountains alluvium in deep struam cuts. Lehi Terrace. Flooding common during major storms. BF BFM over Leh l Terrace deposits. BF M - Thickenin g wHrlge lup t o 40 It 112.2 m]) of alluvium f rom South BFS Mountains and Papago Pari< pediment over Mesa Terrace deposits, obscur­ ing scarp. BFS - Distal ends of alluvial Fa ns from McDowell M oun tain s or from Lehl Terrace - Paired alluvial terraces representing a former leval of t he Sa lt Camelback Mountain and Papago Parte: Ped iment over 5awik Terrace Rivel floodplam before a change III stream regimen caused the river to cut deposits. Bedrock highlands - lsolaled bedrock knobs and inselbergs locally covered down t hrou~h its own dep osits. The terrace is ap proximately 5 h 11.5 m) by a t hi n (lw..s than 2 tt (O.6 m J) VCIlCCI of talus mId collU Vium. Slopes above the present river channel. and was flooded by exceptional flows prior BH generally exceed 15%. Topography IS rugged and steep w ith elevations up 10 to the construction of reservoirs upstream. The back scarp between this and 1745 It (529 m) at op Barnes Butte, the highest point in the quadrangle. Well the older Mesa Terrace marks the limit of flooding. The terra ce remnants drained with flooding conlined to steep mountain washes. A ctive alluvial fan se gments - Gently sloping sur1ac es I less t han 5% ). Un­ LT range from 0.5 to 2.0 miles (610 10 3,220 ml in width, and are boulldoo by a dul

Mesa Terral:e - Paired allu vial tEl rraCtl rern llanlli representing a former level of the Sa lt River f loodplain. Gently sloping (0 to 2% I. slightly undulaling sur­ Inactive alluvial fan ~0l:lme ll ts - Gently sl oping s u rf~cus Iseldom ()x{)oodlng l ace of low relief. Flva to 10 It 11 .5 to 3 m) scerp forms boundary between 5% ). Land surface undulatory with less then 5 ft \1.5 m l relief, except near this and the younger Lehl Terrace , except locally where concea led beneath a strc3m r:h annElls which m Oly be incised up to 15 h (46 m). Stro nf)ly MT wedge-shaped bla nket of sediment from South Mountains and Pap890 Park d eveloped ca liche VISible In stream c ul s. Well drained, f looding generally Pediment. Caliche st ron gly developed in the terrace deposits. InCised 10 It conf ined to channels. 13m) by Granite Reef W ash, which floods during major storms. Natural drainage poor south of Salt River.