Hess Mine - Picacho - Laguna Dam.kml

Hess Mine - Picacho - Laguna Dam

Picacho

Regional Maps

Jpg image

Picacho State Rec. Area, jpg image
Jennifer Lynn Nielsen, 2004. STRUCTURAL GEOLOGY OF PICACHO STATE RECREATION AREA:IMPLICATIONS FOR THE TRANSFER OF BAJA CALIFORNIA TO THE PACIFIC PLATE
A Thesis Presented to the Faculty of San Diego State University
Bachelor of Science
Gary H. Girty, Douglas Stephenson, Adam Canfield, Jeff Marsh, Tim Middleton, Jonathan Rayburn, Matthew Sisk, Danielle Verdugo, Robert Moniz, Jeremiah Gunter, Jennifer Nielsen, Christina Gasca, Andrea Rowland-Smith, Mindy Smith, Krissy Lovering, Kerry Campbell, Flavio Castenada, Ryan Gray, and Cameron Campbell
GEOLOGY OF PICACHO STATE RECREATION AREA, SE CALIFORNIA: IMPLICATIONS FOR THE TIMING OF FORMATION OF THE CHOCOLATE MOUNTAINS ANTICLINORIUM
Department of Geological Sciences, San Diego State University San Diego, California 92182

Winterhaven seds.
Winterhaven Formation
Latest Cretacious - Earliest Tertiary
The chlorite-grade greenschist facies Winterhaven Formation is subdivided into metavolcanic and metasedimentary units (Figs. 3 and 4). The ~80-m-thick metavolcanic unit is composed almost entirely of massive, highly jointed and fractured, aphanitic to porphyritic and locally amygduloidal, trachybasalt to trachyandesite flows (Haxel et al., 1985). Overlying the metavolcanic unit is ~360 m of metamorphosed quartz and feldspathic arenite, crudely foliated argillite, and stretched pebble conglomerate (Haxel et al., 1985). The metamorphic assemblage in the Winterhaven Formation is dominantly quartz + albite + white mica + chlorite + epidote ± calcite.

Winterhaven volc.

Orocopia Schist

Dioritic Gneiss

Picacho State Recreational Area, via internet
GEOLOGY OF PICACHO STATE RECREATION AREA
Gary H. Girty, Douglas Stephenson, Adam Canfield, Jeff Marsh, Tim Middleton, Jonathan Rayburn, Matthew Sisk, Danielle Verdugo, Robert Moniz, Jeremiah Gunter, Jennifer Nielsen, Christina Gasca, Andrea Rowland-Smith, Mindy Smith, Krissy Lovering, Kerry Campbell, Flavio Castenada, Ryan Gray, and Cameron Campbell
Department of Geological Sciences
San Diego State University
San Diego, California 92182
Google Earth Overlays
Tony Carrasco

Samples

Maps and Overlays

Legend

Geologic Map
PICACHO STATE RECREATIONAL AREA

Oricopia Schist
Photo Credit: Jennifer Nielsen 2004

Basaltic andesite of the Quechan volcanics
Photo Credit: Jennifer Nielsen 2004

Bear Canyon Upper Member
Photo Credit: Gary Girty 2005

Ferguson Wash Ignimbrite
Photo Credit: Gary Girty 2005

Bear Canyon Lower Member
Photo Credit: Gary Girty 2005
Clast Count

Field Photos

Picture taken from the road looking east toward the hills composed of Rojo Grande Trachyte

Bear Canyon Panoroma

Looking Southwest at Picacho Peak
Photo Credit: Jennifer Nielsen 2004

Faulting of the Ignimbrites of Fugerson Wash and the overlying Bear Canyon Conglomerate

Unit Descriptions

Tbcu
Bear Canyon Conglomerate - Upper Member
Pre-Middle or Pre-Late Miocene
Unconformably overlying the lower and middle members are variably thick flat lying polymictic gravel beds of the upper member (Fig. 3). Clasts in the upper member are derived from both the metamorphic basement complex and the overlying Oligocene volcanic succession. It has not been studied in detail, but clearly has not been tilted as have the underlying middle and lower members. Sherrod and Hughes (1993) state that “aggradation in the Picacho State Park area had largely ceased before eruption of basalt lava at Black Mountain”. Black Mountain lies just to the NW of Picacho. Two K-Ar dates for the basalt at Black Mountain are 13.4 +/- 2.6 Ma and 9.6 +/- 1.8 Ma. The basalt of Black Mountain appears to be interstratified with the flay-lying upper member of the Bear Canyon conglomerate. Taken as a whole these data along with the argument of Sherrod and Hughes (1993) suggest that the lower and middle members of the Bear Canyon conglomerate were deposited sometime prior to either ~13.4 (Middle Miocene) or ~9.6 Ma (early Late Miocene) and after about ~25 Ma (late Oligocene).

Tbcm
Bear Canyon Conglomerate - Middle Member
Pre-Middle or Pre-Late Miocene
The middle member fills 2 to 7 meter deep channels cut into the lower member, and is tilted about 15o to the NW (Figs. 3 and 4). It is variable in thickness but locally reaches ~200 m. Though it has not yet been studied in detail, it is dominated by paraconglomerates and orthoconglomerates containing as much as 30-40% rounded dioritic and mylonitic dioritic clasts, as well as 5-10% highly weathered mica schist fragments derived from the Orocopia Schist.

Tbcl
Bear Canyon Conglomerate - Lower Member
Pre-Middle or Pre-Late Miocene
The lower member, composed mostly of poorly sorted paraconglomerates derived from debris flows and orthoconglomerates derived from sheet flood deposits, is tilted on average ~21o NW (Fig. 3). It thickens to the NW where our cross section suggests a thickness of over 300 m (Fig. 4B). Within the lower member gravel-sized clasts are sub-round to sub-angular ranging in size from boulders to pebbles. In addition, ~5 to ~10 m thick laterally discontinuous sandstone-rich intervals occur in the approximately lower, middle, and upper portions of the lower member.

Twa
Walker Andesite
Oligocene
Crowe (1978) subdivided the rhyodacite of Little Picacho Peak into a lower unit composed mostly of rhyodacitic to rhyolitic flows, domes, and plug domes and an upper unit composed of pyroclastic material. In contrast, our work suggests that the lower unit consists of three chemically distinctive and mappable units, none of which are rhyodacites or rhyolites on the revised trace element plot of Winchester and Floyd (1977) (Fig. 5) (Girty et al., 2005a). These three units, from oldest to youngest, are the Marcus Wash trachyte, the Rojo Grande trachyte, and the Walker andesite. Field relationships suggest that all three units were emplaced as a series of WNW-trending composite domes, or plug domes (cf. Crowe, 1978).

Tifw
Ignimbrites of Fugerson Wash
Oligocene
The ignimbrite of Ferguson Wash forms a multiple-flow, single-cooling unit with zonal variations typical of major ash-flow sheets (Crowe, 1978). It is crystal poor, with broken crystals of plagioclase, sanidine-anorthoclase, biotite, and oxides. Vitric constituents include mostly pumice fragments and shards. Fresh glass is rare, and devitrification locally obliterates vitroclastic textures. K-Ar data indicate that the ignimbrite of Ferguson Wash was erupted ~27-25 Ma (Crowe, 1978; Sherrod and Hughes, 1993).

Twwt
White Wash Trachyte
Oligocene
The White Wash trachyte overlies and locally forms pyroclastic dikes or plugs intruding the ignimbrite of Ferguson Wash and the Rojo Grande trachyte. On the revised trace-element magma-series discrimination diagram of Winchester and Floyd (1977), it has a unique chemistry that does not overlap the chemistry of other trachytes mapped during our study.

Tpu
Bedded Pryoclastic Undifferentiated

Trgt
Rojo Grande Trachyte
Crowe (1978) subdivided the rhyodacite of Little Picacho Peak into a lower unit composed mostly of rhyodacitic to rhyolitic flows, domes, and plug domes and an upper unit composed of pyroclastic material. In contrast, our work suggests that the lower unit consists of three chemically distinctive and mappable units, none of which are rhyodacites or rhyolites on the revised trace element plot of Winchester and Floyd (1977) (Fig. 5) (Girty et al., 2005a). These three units, from oldest to youngest, are the Marcus Wash trachyte, the Rojo Grande trachyte, and the Walker andesite. Field relationships suggest that all three units were emplaced as a series of WNW-trending composite domes, or plug domes (cf. Crowe, 1978).

Tmwt
Marcus Wash Trachyte
Crowe (1978) subdivided the rhyodacite of Little Picacho Peak into a lower unit composed mostly of rhyodacitic to rhyolitic flows, domes, and plug domes and an upper unit composed of pyroclastic material. In contrast, our work suggests that the lower unit consists of three chemically distinctive and mappable units, none of which are rhyodacites or rhyolites on the revised trace element plot of Winchester and Floyd (1977) (Fig. 5) (Girty et al., 2005a). These three units, from oldest to youngest, are the Marcus Wash trachyte, the Rojo Grande trachyte, and the Walker andesite. Field relationships suggest that all three units were emplaced as a series of WNW-trending composite domes, or plug domes (cf. Crowe, 1978).

Tqv
Basaltic Andesites of the Quechan Volcanics
Oligocene, 33-27 Ma
The oldest Tertiary volcanic unit in and around Picacho is the 33 Ma to 27 Ma Quechan volcanics (Figs. 3 and 4) (Crowe, 1978; Sherrod and Hughes, 1993). Composed of lava flows, flow breccia, and lesser amounts of laharic breccia, the Quechan volcanics have a composite thickness of more than 300 m.
Texturally, the Quechan volcanics are porphyritic with phenocrysts of mostly plagioclase and lesser amounts of pyroxene set in a pilotaxitic to felsophyric groundmass of plagioclase, oxides, and cryptocrystalline material. Though Crowe (1978) claimed that the Quechan volcanics were dominantly rhyodacites none of the samples that were analyzed during our studies are rhyodacitic in composition on the revised trace-element magma-series discrimination plot of Winchester and Floyd (1977) (Fig. 5) (Girty et al., 2005a). In the field, the dark gray to black color of the Quechan volcanics stands out in stark contrast to the browns and lavender colors of the overlying unit mapped by Crowe (1978) as the rhyodacite of Little Picacho Peak.

Te
Pre-Quechan Alluvial Deposits
Eocene?
Unconformably overlying the Winterhaven Formation is a discontinuous and variably thick sequence (up to ~35 m) of mostly paraconglomerate to very coarse sandstone that locally includes white thinly bedded to laminated tuffaceous granular to coarse grained sandstone (Figs. 3 and 4). In addition, an ~3-m-thick section of limestone has been observed in one area to form the lower portion of this sequence (G.H. Girty, unpublished observations). Crowe (1978) mapped these rocks as a prevolcanic fanglomerate while Sherrod and Hughes (1993) referred to them as arkosic sedimentary strata.
Beds of paraconglomerate range from 0.5 m to 2.0 – 3.0 m in thickness, while sandstone beds vary from 0.25 to 1.0 m. Conglomerate beds exhibit both inverse and normal grading though massive beds are locally prevalent. Clasts in conglomerates are invariably derived from the Winterhaven Formation and include both metavolcanic and metasedimentary varieties as well as rounded fragments of mylonitic gneiss and pink colored equigranular leucogranite.
White, tuffaceous granular to coarse grained sandstones are composed of a poorly sorted framework of angular quartz, feldspar, and volcanic rock fragments. Beds vary from 1.0 cm to ~10 cm in thickness.

T-Cos
Orocopia Schist
Latest Cretacious - Earliest Tertiary
In and around Picacho the Orocopia Schist is recrystallized to an assemblage dominated by biotite + albite + quartz + white mica ± epidote ± chlorite. In thin section chlorite and epidote record a retrograde event as they replace biotite and plagioclase respectively, while biotite, albite, quartz, and white mica appear to represent the remnants of a prograde assemblage. These relationships and interpretations are consistent with those made by Jacobson et al. (2002, in press) and imply that only the structurally higher chlorite-zone of these authors is preserved at Picacho.

T-Cos
Orocopia Schist
Latest Cretaceous - Earliest Tertiary
In and around Picacho the Orocopia Schist is recrystallized to an assemblage dominated by biotite + albite + quartz + white mica ± epidote ± chlorite. In thin section chlorite and epidote record a retrograde event as they replace biotite and plagioclase respectively, while biotite, albite, quartz, and white mica appear to represent the remnants of a prograde assemblage. These relationships and interpretations are consistent with those made by Jacobson et al. (2002, in press) and imply that only the structurally higher chlorite-zone of these authors is preserved at Picacho.

Jwh
Winterhaven Formation
Latest Cretacious - Earliest Tertiary
The chlorite-grade greenschist facies Winterhaven Formation is subdivided into metavolcanic and metasedimentary units (Figs. 3 and 4). The ~80-m-thick metavolcanic unit is composed almost entirely of massive, highly jointed and fractured, aphanitic to porphyritic and locally amygduloidal, trachybasalt to trachyandesite flows (Haxel et al., 1985). Overlying the metavolcanic unit is ~360 m of metamorphosed quartz and feldspathic arenite, crudely foliated argillite, and stretched pebble conglomerate (Haxel et al., 1985). The metamorphic assemblage in the Winterhaven Formation is dominantly quartz + albite + white mica + chlorite + epidote ± calcite.

Jg
Dioritic Gneiss
Jurassic?
Probable Jurassic mylonitic orthogneiss (minimum age ~144 Ma, unpublished U-Pb zircon age; Haxel et al., 1985; Haxel et al., 2002; Haxel, personal communication, 2003)

Publications

Thesis
STRUCTURAL GEOLOGY OF PICACHO STATE RECREATION AREA:
IMPLICATIONS FOR THE TRANSFER OF BAJA CALIFORNIA TO THE PACIFIC PLATE
A Thesis
Presented to the
Faculty of
San Diego State University
In Partial Fulfillment
of the Requirements for the Degree
Bachelor of Science
in
Geological Sciences
by
Jennifer Lynn Nielsen
Spring 2004
PURPOSE
Since the geotectonic development of the Western Cordillera has been occurring continuously since the birth of the planet, geologists studying the Cordillera have realized that complete understanding of one increment of growth requires knowledge of what happened before. Mountain building in the Western Cordillera during the Sevier orogeny began in the late Jurassic and Early Cretaceous. A palinspastic reconstruction, modified from Saleeby (2003), shows the geotectonic belts created during the Sevier orogeny, including an offshore trench, the Franciscan accretionary wedge complex, the forearc basins of Sacremento and San Joaquin valleys, the Sierra Nevada magmatic arc, a very complicated hinterland, the Rocky Mountains fold and thrust belt in Nevada and Utah and to the east, the synclinal trough of the Rocky Mountains peripheral basin. A cross section across these various geotectonic elements at approximately 38º North latitude shows the subducting oceanic plate descending at approximately 20-30º beneath the more buoyant continental North American plate).
Following the Sevier event, the angle of the subducting plate shallowed to less that 10º. This shallowing in slab dip had a profound effect on the development of structures in the continental interior. For example, in Colorado, Nevada and Utah, basement core uplifts formed, while in northeast Arizona, southeast Nevada, southwest Colorado and northeast New Mexico, large monoclines developed. Closer to the pacific margin, a large segment of the Sierra Nevada magmatic arc was breached and moved westward.
Though it is difficult to specify exact timing, arc magmatism sweeps eastward in the late Cretaceous through early Tertiary time. Following the low angle slab event, the inclination of the slab steepened and arc magmatism migrated back to the west. It was this back sweep of arc magmatism that produced the breached segment, sometime during latest Cretaceous (Saleeby 2003).
Although the early history of the Western Cordillera is complex, greater complexity followed. For example, between 21 to 10 Ma, the eastern margin of the Western Cordillera, from Idaho to Mexico, underwent large-scale extension. This extension was produced primarily by the influx of basaltic magma, which heated and weakened the crust (Gans et al. 1989) (Figure 4). The influx of basaltic magma produced partial melting and hybridization of the lower crust, culminating in large-scale volcanic eruptions and extension. During the final stage of extension, Gans (1989) shows the development of metamorphic core complexes, which are found throughout the Colorado River extensional corridor. Following the development of the core complexes, Baja California is transferred from the North American to the Pacific plate approximately 6 to 12 Ma. The mechanism by which this transfer occurred remains controversial.
Stock and Hodges (1989) have suggested that the transfer of Baja California to the Pacific plate took place through partitioning of movement into a strike-slip component along the Tosco-Abrejos fault and northwest – southeast extension in the Gulf Extensional Province. If the model proposed by these authors is correct, we should observe large scale extensional structures developing between 6 and 12 Ma in the southeastern corner of California. In contrast, Gans (1997) proposes that following the westward back sweep of arc magmatism and large scale extension, the transfer of Baja California occurred 6 - 12 Ma through a pronounced distributed dextral shearing event. If the model of Gans (1997) is correct, then we would expect to observe large dextral – sense strike – slip faults in the southeastern corner of California. The purpose of this thesis is to assess which of these two models is most consistent with the structural evolution of Picacho State Recreation Area.

Publication
GEOLOGY OF PICACHO STATE RECREATION AREA, SE CALIFORNIA: IMPLICATIONS FOR THE TIMING OF FORMATION OF THE CHOCOLATE MOUNTAINS ANTICLINORIUM
Gary H. Girty, Douglas Stephenson, Adam Canfield, Jeff Marsh, Tim Middleton, Jonathan Rayburn, Matthew Sisk, Danielle Verdugo, Robert Moniz, Jeremiah Gunter, Jennifer Nielsen, Christina Gasca, Andrea Rowland-Smith, Mindy Smith, Krissy Lovering, Kerry Campbell, Flavio Castenada, Ryan Gray, and Cameron Campbell
Department of Geological Sciences
San Diego State University
San Diego, California 92182
ABSTRACT
The Chocolate Mountains anticlinorium has been interpreted to be an ~50-60 Ma fault-bend fold related to the low-angle subduction of a segment of the Farallon plate or, alternatively, a post-24 Ma Miocene fold associated with exhumation during extension. At Picacho State Recreation Area, the anticlinorium forms an upright west-trending fold plunging moderately to the west. Folded about the anticlinorium is a section of Oligocene volcanic rocks that include the Quechan volcanics (~33-27 Ma), trachyte of Marcus Wash, trachyte of Rojo Grande, bedded pyroclastic material, trachyte of White Wash, Walker andesite, and ignimbrite of Ferguson Wash (~25 - ~27 Ma). Sixty eight samples collected from throughout the Oligocene volcanic section were analyzed for major and trace elements. On the conventional TiO2/Zr versus Nb/Y magma series discrimination diagram specimens from each unit cluster tightly together forming non-overlapping unit-dependent compositional fields. On the northern limb of the Chocolate Mountains anticlinorium, the Bear Canyon conglomerate unconformably overlies the ignimbrite of Ferguson Wash, and is subdivided into three unconformably bounded members. The lower member is tilted 21o NW. An embayment formed by the contact between the lower member and the ignimbrite of Ferguson Wash may represent the remnants of a feeder canyon branching SE toward the trace of the Chocolate Mountains anticlinorium. Gravels in the lower member are characteristically composed of three texturally distinctive groups, each group also displaying a different range of colors. Chemical analyses of 12 characteristic clasts collected from these three distinctive groups of clasts indicate derivation from the ignimbrite of Ferguson Wash, the Walker andesite, and the Quechan volcanics. Though most clasts in the lower part of the lower member are texturally and chemically similar to the ignimbrite of Ferguson Wash a small proportion may have been derived from bedded pyroclastic material lying stratigraphically beneath the ignimbrite. In contrast, the clast population in the middle and upper parts of the lower member contains progressively greater proportions of the Quechan volcanics, along with a small percentage of clasts derived from the Walker andesite. Eleven analyzed sandstone samples collected from the lower, middle, and upper parts of the lower member on a plot of TiO2/Zr versus Nb/Y spread within a triangular region whose apices are formed by the average compositions of the Quechan volcanics, Walker andesite, and ignimbrite of Ferguson Wash. In addition, the compositions of sandstone samples overlap the compositional field defined by 28 samples analyzed from the Orocopia Schist, and 8 samples analyzed from the metasedimentary member of the Winterhaven Formation. Though the middle member has not yet been studied in detail it dips ~15o NW, and is dominated by conglomerates with dioritic and mylonitic dioritic clasts along with fragments of the Orocopia Schist. The upper member is flat lying and polymictic. It contains clasts derived from both Mesozoic rocks and Tertiary volcanics that are common throughout the Picacho region. At Black Mountain the upper member is interstratified with basalts that have reported K-Ar ages of 9.6 and 13.4 Ma. The above data indicate that at Picacho the Chocolate Mountains anticlinorium formed sometime between 25 and 9.6-13.4 Ma, and was likely growing during deposition of the lower two members of the Bear Canyon conglomerate. We therefore conclude that the history of the anticlinorium outlined above can not be associated with the much older low-angle subduction of the Farallon plate.
Pacific Section SEPM book #101:
USING STRATIGRAPHY, SEDIMENTOLOGY, AND GEOCHEMISTRY TO UNRAVEL THE GEOLOGIC HISTORY OF THE SOUTHWESTERN CORDILLERA:
a Volume in Honor of Patrick L. Abbott
Girty, G. H., and Cooper, J. D. (eds.), 2006, 328 pages (50 in color), ISBN 1-878861-94-8
Pacific Section SEPM

Cross Sections

A-A'
CROSS SECTION A-A'

symbols

CROSS SECTION A-A'

A - A'
CROSS SECTION A-A'

Picacho Mine region_losh_map

Picacho Mine region_losh_lgnd

Picacho Mine

Picacho Mine map - Richard and Spencer, 1969. Arizona Geol. Survey
Geologic Map of the Picacho Mine area, Southeastern California
Richard, S.M. and Spencer, J.E. 1996. Arizona Geological Survey, Open File report 96-30.

Picacho Mine Map units

Picacho Mine Map-area sections

Imperial Dam map - Richard S. M., 1992, Arizona Geological Survey

Jnct Picacho rd & Ross Rd

Picacho Rd bridge

Ross Corner Store

OPTION Hess Mine region

Map A - Hyperion data, Zhang, 2005

Map B - Morton, 1977 & Zhang, 2005

Jnct 95 and road into Laguna dam

Hess jnct imperial rd with road to Hess

Hess jnct north rd to Hess and rd SW to Br outcrop

Hess Imperial rd - Senator rd bridge over canal

Hess Squaw Lake campsite

Hess jnct Senator Wash rd and road into Hess

Hess Mine

Mine

Hess end of rd to gabbro

End of rd; trail to Gabbro/dikes

Gabbro and mafic dikes - ophiolite?

Hess - calcrete block