Stratigraphy of the Waterman and Silver Bell Mountains
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FIGURE 45. Generalized geologic map and diagrammatic cross sections of Wate rman and Silver Bell Mountains, Pima County, Arizona, showing part of route of Field Trip II. WaterITlan-Silver Bell-Trip II
STRATIGRAPHY OF THE WATERMAN AND SILVER BELL MOUNTAINS
TRIP II, ROAD LOG
Thursday, April 2, 1959
Leaders: N. E. McC1YITlonds, H. G. Page, and C. W. Haynes
Driving distance: 87. 4 ITliles Logged di stanc e: 49. 7 ITliles
. General StateITlent
The principal purpose of thi s trip is the exaITlination of the Paleozoic section in the WaterITlan Moun tains. In addition, the party will exaITline Cretac eous (?) sediITlents in the pass between the WaterITlan and Silver Bell Mountains and the Oxide Pit of the Silver Bell ITline. The route of the trip will go around the north end of the Tuc son Mountains (Trip III) , cross Avra Valley, into the WaterITlan and Silver Bell Mountains and return froITl Silver Bell by the saITle route (fig. 55). The trip will include a leisurely 2- to 3-hour hike through the Paleozoic section of the WaterITlan Mountains and a 30 -ITlinute walk to the Cre tac eous (?) rocks.
0. 0 JUNCTION of Speedway Boulevard and State Highway 84, alternate. TURN o. c RIGHT.
5 0. 5 8:00 to 11:00: The Tuc son Mountains (Trip IV) are here fo r the ITlo st part rep o. resented by a dip slope of Cat Mountain rhyolite flows and welded tuff-aggloITlerate.
1. 8 2. 3 JUNC T ION with State Highway 93. Watch for ITlerging traffic . Divided highway begins in O. 5 ITliles.
0. 6 2. 9 3:00: The Santa Catalina Mountains rise to an altitude of 9, 150 feet, about 6, 900 feet above altitude of the highway. The Santa Catalina Mountains (Trip III) are cOITlpo sed ITlainly of gneiss, schi st, and various intrusive rocks.
2. 4 5. 3 Santa Cruz River bed in near ITliddle-ground to left. The Santa Cruz River is distinctly aSYITlITletrical in the reach along the Tuc son Mountains, probably ow- ing to a greate r ITlass of alluvial debris cOITling froITl the Santa Catalina Moun tains, which are higher and have a greater bulk than the Tucson Mountain s. North of the Tuc son Mountains, the Santa Cruz River is ITlo re centrally located on the plain between the sITlaller and ITlore equally :::ized Tortillita Mountains to the east, which can be seen at 2:00, and ITlountains to the west.
0. 8 6. 1 9:00: Several sITlall hill s, located just this side of the ITlain ridge of the Tuc son Mountains, are cOITlposed of Paleozoic liITlestone ranging in ag e froITl Missis sippian to PerITlian. The Paleozoic rocks rest on Cretaceous (?) volcanic and sediITlentary rocks and have been interpreted as klippe (Brown, 1939; Whitney, 1957) and as reITlnants of a giant sediITlentary breccia (Kinnison, E). 6 6. 7 Bridge over Rillito Creek, the tributary of the Santa Cruz River that drains the o. southe rn front of the Santa Catalina Mountains and the ranges that ring Tucson to the east and southeast.
6 7. 3 9:00: Wasson Peak, altitude 4, 677 feet, is the highe st point in the Tuc son Moun o. tains. Wasson Peak and its higher slopes are cOITlpo sed of arkosic Creta ceous (?) sediITlents intruded by granite and quartz ITlonzonite stocks and large latitic sills. A faint color and texture chang e to the south ITlarks the contact between the se rocks and the overlapping Cat Mountain rhyolite. At 10:30 is Safford Peak, which ha s been interpreted as a volcanic neck (Brown, 1939) cOITlpo sed of light gray dacite with proITlinent vertical flow structure. The area of the peak is elliptical, elongated along a N. 600 E. axis. The dacite plug pierces the sur rounding volcanic and sediITlentary rocks and is considered to be the youngest igneous cock at the north end of the Tuc son Mountains.
O. 5 7. 8 Bridge over Canon del Oro Wash, the tributary of the Santa Cruz River that drains the northwe stern part of the Santa Catalina Mountains. Canon del Oro
213 Trip II- Waterman-Silver Bell
Wash was considered by Davis (1931) to have pirated a considerable portion of the northern slopes of the Santa Catalina Mountains which previously had drained northeastward into the San Pedro Valley.
2. 6 10. 4 Cortaro, altitude 2, 155 feet. Road to left leads over a low gap south of Safford Peak and continues to the Arizona-Sonora Desert Museum, which specializes in presenting the natural history of the southwest. At 2:00 are the Tortillita Moun tains, a low, deeply dissected range compo sed principally of metamorphic and igneous rocks. The Tortillita Mountains, perhap s because of their apparently gently rolling topography, are popularly described to visitors as the "olde st" mountains around Tuc son.
3. 7 14. 1 SLOW. Left turn ahead. Move into left-hand lane .
0. 2 14. 3 TURN LEFT onto Avra Valley road. STOP before crossing south bound highway .
O. 1 14. 4 Left of the road is the American Smelting and Refining Co. loading apparatu s for concentrate coming from the Silver Bell mine. Conc entrate is brought from the mill at Silver Bell in trucks and loaded here onto railroad cars to be shipped to El Pa so, Texas, or Hayden, Arizona, for processing and refining .
0. 2 14. 6 The brown hills ahead are composed of ande sitic fl ows and breccias and form a north-trending ridge. A probable extension of thi s ridge can be seen at 2:30, about 3 miles north, whe re a low dark hill of Cretaceous (?) sedimentary rocks (Brown, 1939) pokes up through the alluvium. Alluvium cove rs the intervening portion of the ridge, known as the Rillito Narrows, who se presenc e is confirmed by water-table altitudes and other ground-water data.
0. 4 15. 0 1:00: Arizona Portland Cement Co. plant.
0. 4 15. 4 Bridge over the Santa Cruz River. The drainage basin of the Santa Cruz River forms one of the large drainage areas tributary to the Gila River, who se main stem lies about 60 miles north. Only following periods of greater than normal rainfall, however, does flow go north beyond the Rillito Narrows.
O. 1 15. 5 At left is a road cut in brecciated and tilted massive andesite flows.
0. 2 15. 7 CAUTION at road crossing . The crossing road runs between the cement plant and the Picacho de Calera, or Twin Peaks, which are mined for limestone. These hill s are compo sed of Precambrian schist, Paleozoic clastic and lime stone strata and post-Cretac eous granite (Bryant, 1952). The structu re of the Twin Peaks rocks ha s been interpreted as a klippe resting on Cretaceous (?) rocks (Brown, 1939), and as the west limb of an intricately deformed syncline which passes beneath the Tuc son Mountains (Britt, 1957). The small hill no rth of Twin Peaks is composed of the Pennsylvanian Horquilla formation overlying Permian lime stone along a gently northeast-dipping fault. The quarrying opera tions are presently cutting into Horquilla and Mississippian Escabrosa limestone.
1. 9 17. 6 Across the broad expanse of Avra Valley are the Roskruge Mountains between 9:30 and 11:00, the Waterman Mountains at 11:30, and the Silver Bell Mountains from 12:00 to 1:00. The tailing s dump of the Silver Bell mine can be seen at the south end of the Silver Bell Mountains. To the southwest, at a much greater distance, are the Coyote- Quinlan Mountains, and to the northwest, at about 2:00, are the Picacho Mountains with Picacho Peak at their southern end. Picacho Peak, a bilingual redundancy -- "pichacho" means "peak" in Spanish -- was a prominent landmark during the early explorations of this country. It is compo sed of a complex of small fault blocks of volcanic flows (Feth, 19 51), although it was long believed to be a deeply dissected volcanic neck. The mass of Picacho Moun tain to its north is compo sed of gneissic and intrusive rocks.
1. 6 19. 2 Diagrammatic cross-sections between southern Tuc son Mountains at 8:00 and the Roskruge Mountains (A-A '), in the lower ho rizon at 10:00, and between the Ro skruge Mountains and the Coyote- Quinlan Mountains (B-B'), at a greater dis tanc e at 10:00, are shown in figure 56.
1. 4 20. 6 Road to right leads to Marana Air Base and the central portion of the irrigated area lying between the Rillito Narrows and Picacho Peak. l
214 0. 9 21. 5 S-curve in road. At 11:30 in the far distance are the Sierrita Mountains, on whose east flanks is the Pima mining district (Trip I) .
2. 4 23. 9 3:00: Cotton mill. Avra Valley cotton growers rank among the highest bale-per acre produc ers the State, with 4 bales per acre being common. in O. 5 24. 4 Large dip across a channel of Brawly Wash, the principal wash draining Avra Valley. Brawly Wash fo-.:'ms an intricate distributary paralleling that of the Santa Cruz River between here and the vicinity of Picacho Peak, where they join.
3. 1 27. 5 Main channel of Brawly Wash.
1. 0 28. 5 12:00: Waterman Peak, altitude 3, 820 feet, highe st point in the Waterman Moun tains. The general geology of the area ahead is shown on figure 19, and the cross-section passes through the Waterman and Silver Bell Mountains as they are seen ahead.
1. 1 29. 6 Road junction and cattleguard. Road to left leads to one of the El Paso Natural Gas Co. pumping stations along the natural gas line from Texas to California. The hills from 9:00 to 10:30 and from2:00 to 3:00 are composed of volcanic alluvial sediments capped by ande sitic and basaltic flows, both of which dip at low angles to the east. They form a belt flanking the east slopes of the Waterman and Silver Bell Mountains. Isolated hill s of similar volcanic flnws, but dipping generally to the west, are located on the west flank of the se mountains. At 2:00 is a high ser rate knob known as Ragged Top or Wolcott Peak. It is a volcanic neck of silicic composition located along a structural break between Precambrian granite and Cretaceous (?) intrusive and volcanic rocks. There are several intrusive bodies along this same generally east-west trend.
0. 7 30. 3 Cross El Paso Natural Gas Co. pipelines.
2. 7 33. 0 Road cut in Cretaceous (?) rocks to right.
0. 4 33. 4 TURN LEFT onto unimproved road.
O. 5 33. 9 Road to right leads to Indiana-Arizona mine, a copper, lead, zinc . silver mine, discovered in 1880. This mine was operated from 1942 to about 19 52, and has shipped several thousand tons of ore. Mo st mineralization wa s in the form of sulfide and carbonate vein deposits, emplaced during the Tertiary period pri marily into the Cambrian formations along east to northeast-trending faults (Ruff, 1951) .
O. 1 34. 0 STOP at gate. Last car through please close gate . The Waterman Mountains (McClymonds, 15) form the circle of hills to the front. The southe rly dipping hogback at 11:OOi s capped by Permian Concha formation (fig . 20B). Waterman Peak, at 1:30, is composed of an Escabrosa lime stone cap resting in fault con tact on the Cambrian Troy quartzite (fig. 20A, C). Starting with the Troy, the section is in no rmal sequence toward the northeast (fig . 21), although several faults cut out parts of the section. The large ridge in front is composed of Concha limestone, dipping ste eply to the north, with Permian Rainvalley forma tion forming the dip slope on the east end. The ridge is in fault contact with Cretaceous (?) sedimentary rocks which dip under the Paleozoic rocks along a high-angle reverse fault and form the lower slopes. The ridge between 1 :30 and 2:30 is composed of Mississippian to Permian formations. At the northwest end of the ridge the Horquilla formation is faulted against Cretaceous (?) sediments. Enter area shown on figure 7.
1. 5 35. 5 Road to right; continue straight ahead.
O. 3 35. 8 Road to left; keep straight ahead. The top of the rugged hill is fo rmed of steeply northeast-dipping Concha limestone. Halfway down the right (north) side is the Rainvalley formation. The dark zone within the Rainvalley is composed of chert nodules and forms a prominent marker bed. North of the hill, the steep valley is eroded along a large scisssors fault, with the south side downthrown, whose displacement of more than 1, 000 feet at the east end is reduced to less than 100 feet at the west end.
l 215 O. 1 35. 9 Junction with road from right.
O. 1 36. 0 The ridge on the left side of the road is composed predominantly of silicified Concha limestone. The road here traverses the approximate location of a prob able strike- slip fault with aN. 750 E. trend (fig. 8B). Displacement along this strike-slip fault is left lateral and apparently in the magnitude of about 2 miles.
0. 3 36. 3 3:00: A good view of the southeast face of the hill discussed at mileag e 35. 8. In the saddle south of the hill, the upper part of the Scherrer formation crops out, but the lower part is cut out by a fault. The hill left and south of the saddle is composed of Colina limestone and the far slope is composed of the Andrada formation. Escabrosa limestone and Martin and Abrigo formations crop out in the hill s ahead. The lower slopes to the right are cut on Precambrian (?) granite, which apparently is faulted against the Paleozoic rocks.
O. 1 36. 4 Abandoned ranch house; keep to left. Granite is exposed in dug well. The road passes through a low ridge composed of Concha lime stone. The middle lime stone member of the Scherrer formation crops out in the slope to the left of the road at the north end of this small pass at about mileage 36. 5.
0. 2 36. 6 Road junction. Turn right. The road straight ahead leads into the Papago Indian Reservation and around the southwestern end of the Waterman Mountains .
O. 1 36. 7 Low hill immediately right of road is capped by Concha limestone which over lies the upper member of the Scherrer formation on a low-angle thrust fault.
O. 1 36. 8 Hill to the left of the road is made up of the lower sandstone member of the Scherrer formation. The road here again crosses the approximate location of the postulated strike- slip fault discussed at mileage 36. O.
0. 4 37. 2 STOP 1. Dismount. Proceed on foot on road to abandoned mine on south fac e of Waterman Peak (fig. 20A, C). The approximate route of the foot traverse and the Paleozoic rocks that will be seen along it are shown on the geologic map and cross section in figure 21. (The bus will turn around and retrac e its route 1. 4 miles to mileag e 38. 6,
1. 7 38. 9 turn left up an unimproved road for O. 3 mile to m:J.eag e 38. 9 and wait for the return of the field party. Upon return of field party, turn right at 38. 9 and pro ceed 0. 3 mile to mileage 39 .2; turn left and continue 2. 1 miles to the highway whe re the road log continue s at mileag e 41. 3) .
·2. 4 41. 3 JUNC TION. TURN LEFT onto paved highway.
1. 0 42. 3 Road to left leads tc Indiana-Arizona mine .
O. 1 42. 4 Deep dip. Aluminum-painted apparatus at right of road is part of the Silver Bell water system. Three wells in the alluvium of Avra Valley supply most of the Silver Bell water from a water level of about 250 feet, with pumping drawdowns of from 15 to 25 feet. Production from the se wells ha s been as high as 85 million gallons per month, but wa s reduced to about 50 million gallons by recirculating water used in the mill. Declines in the water table since 1952 average about 36 feet. Water is piped about 9 miles from the well field to the mine and townsite through a l2-inch line with one booster station.
the mountain area, water is encountered in all rock types but permeability Inseems highest in altered monzonite. Water at the El Tiro Pit is supplied from a local abandoned shaft and comes mainly from brecciated zones in alaskite. In the vicinity of the Oxide Pit water levels of from 100 to 400 feet are apparently controlled by rock-type and structure more than topography. general, the water is reported as being "acid", and total dissolved solids rangIn e from about 750 to 4, 000 parts per million.
1. 0 43. 4 The narrow, dark, dike-like outcrop s close to and on either side of the road are compo sed of lime stone lense s within Cretaceous (?) sedimentary rocks.
0. 2 43. 6 Tailing from Silver Bell mill at right of road. l
216 1. 3 44. 9 JUNCTION. TURN LEFT on paved road leading to the Silver Bell community. Maroon-colored Cretaceous (?) mudstone, sandstone, and conglomerate are exposed on the right of the road in the deep washes.
0. 3 45. 2 Road crossing . Proc eed straight ahead.
O. I 45. 3 Road crossing . TURN RIGHT. Building on right with adjoining swimming pool is the Am erican Smelting and Refining Co. mess hall. STOP 2. Dismount fo r LUNCH. Lunch will be followed by a discussion of the geology around the Silver Bell mine and a visit to the Oxide Pit.
Looking south from the mess hall steps, the broad slopes of Aguirre Valley can be seen leading up to the Quinlan Mountains on the left and to the South and North Comobabi Mountains on the right. The valley floor on the skyline to the south is at the drainage divide between north drainage into the Gila River and south drain ag e into the Sonora River of Mexico. The hill s above the valley floor are com posed of Tertiary extrusive rocks.
After lunch, proceed straight ahead. Silver Bell mill is at 2:00. This is a 7, 500 ton-per-day mill, processing the ore from the Oxide and EI Tiro pits.
0. 5 45. 8 SHARP LEFT TURN; truck maintenance building s and truck parking areas dead ahead.
0. 2 46. 0 STOP. LEFT HAND TRAFFIC . ALL MINE EQUIPMENT HAS RIGHT -OF-WAY . Oxide Pit entranc e is dead ahead. Proceed 500 feet and TURN LE FT on road going up dumps. The se dumps are divided into areas 0f wa ste rock and low grade ore. When the leaching plant is completed, dump s of low grade ore will be leached to recover copper that could not be recovered profitably otherwise.
O. 6 46. 6 Outc rops directly ahead show copper and iron staining.
0. 4 47. 0 SHARP RIGHT TURN; follow transite pipeline. This pipeline will be used for transporting water from the leaching plant to the dump in the leaching process.
0. 2 47. 2 Aguirre Valley at 3:00.
0. 2 47. 4 STOP 3. Dismount for a short walk to the edge of the Oxide Pit. Stay close to the guide and please don't fall into the pit. A short talk will be given on the occurrence of ore by geologists of the American Smelting and Refining Co. The contact between the oxide and the sulfide zones, intrusive contacts, and fault features can be seen in the pit. To the north, beyond the pit, Paleozoic sedi ments and the Cat Mountain (?) rhyolite are intruded by several igneous bodies. Return to bus and retrace route to the mess �all.
2. 0 49 .4 Mess hall ; proceed dead ahead slowly. WATCH FOR CHILDREN.
0. 2 49. 6 SPEED BUMP. STOP or lose an oil pan. Proceed slowly. At end of road turn left and then right on dirt road behind company houses.
O. 1 49. 7 STOP 4. Dismount for walk to Cretac eous (?) sediment outc rop. The Creta ceous (?) rocks include arko se, mudstone, and conglomerate, which are intruded by ande site and dacite porphyry, quartz monzonite, and alaskite . The conglom erate contains numerous fragments of andesite porphyry and other igneous and sedimentary rocks. After talk, return to bus fo r trip back to Tuc son. Proceed to mess hall corner.
0. 3 50. 0 TURN RIGHT at mess hall corner.
0. 4 50. 4 TURN RIGHT on road to highway from Silver Bell.
22. 7 73. I STOP. TURN RIGHT on State Highway 84, alternate. Follow highway southeast to Tuc son.
14. 3 87. 4 TURN LEFT at Speedway Boulevard; 1. 6 mi. to the University.
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