Thursday, March 26, 2015

THE DESERT AND PRECAMBRIAN ROCKS; CAVE CREEK





At noon in the desert a panting lizard waited for history, its elbows tense, watching the curve of a particular road as if something might happen.               William Safford
               
 During my sojourns to Arizona for the February rock and gem shows, I usually try to camp at, and explore, the numerous state and county parks that dot landscape in the metro Phoenix and Tucson areas.  I have posted on several of these sites including Picacho Peak, the Superstition Mountains, the Santa Catalina Mountains and recently the travertine north of Cave Creek and Carefree. 

Cave Creek is one of my favorite small towns, and by the number of motorcycles and horses on weekends, the favored town of bikers and rodeo fans.  It has some great small watering holes and a plethora of interesting eating joints catering to a wide variety of tastes.  I mean who could pass up a craft brew and a juicy burger at Big Earl’s Greasy Eats.  Cave Creek is trying to hold on to their western style and attitude while keeping down careless zoning and macmansions.  Unfortunately there seems to be a big battle between wantabe developers on Black Mountain and conservationists trying to hold the line on desecration of a beautiful piece of property.  Cave Creek is also home to one of my favorite magazines, True West. 
 
Next door is Carefree, home to massive golf courses and majestic houses and merging into trendy Scottsdale on the south.  The two small towns (C & C) are a contrast in development and preservation.  What they both share, however, is a need to manage urban sprawl, including water resources, extending north from Phoenix and its suburbs.  Cave Creek and Carefree are really the northern boundary of metro Phoenix until one migrates west toward Interstate 17 and the Anthem-New River area.

Valley of the Basin and Range south of Cave Creek/Carefree.  Notice development.

Rugged topography of the Transition Zone north of Cave Creek/Carefree.
One of the reasons for this cessation of urban sprawl to the north is that Cave Creek/Carefree sits at the boundary of the Basin and Range Physiographic Province and the Transition Zone (between the Basin and Range and the Colorado Plateau)--notice photos above.  North of the towns are rugged mountains and plateaus; the physiographic boundary is easily observed.  Only a few non-paved roads extend north from the communities and the major thoroughfare (well a gravel/dirt road anyway) heading to Bloody Basin observes very few homes, certainly no conveniences, and little water before it finally connects with I-17 after jarring 60 miles or so.  The road traverses through a variety of Precambrian igneous and metamorphic rocks with a scattering of Cenozoic volcanics.  Every once in a while an accidental outcrop of Paleozoic rocks  sticks through.   It really is a desolate piece of country; however, that does not mean beauty is absent.  On some of my travels I have simply stopped the vehicle, hopped out and perched myself on a boulder---better to take in the magnificent views and listen to the sounds of “nothing.” 

Everything has beauty, but not everyone sees it.    Confucius
The Basin and Range area from the communities south is characterized by wide valleys with intervening north-south trending fault-bounded (usually) mountain ranges--see photo.  This far south in the Province the ranges are highly eroded and have contributed a huge amount of sediment to the fault-bounded (usually) valleys.   In some localities the mountains have been almost completely buried by the shed sediments.  The rocks in the mountains range in age from Precambrian to Cenozoic.  Many of the valleys contained, at one time or another in the Cenozoic, fresh water lakes and numerous volcanoes and vents spewed out various extrusive igneous rocks (Leighty and others, 1997). 

When sitting in an outdoor cafĂ© in Cave Creek one cannot but help notice the massive high hill blocking the south view from town---Black Mountain.  Unfortunately it seems that “money” can buy property and roads are slowly snaking up the mountain and “spoiling” the views for thousands of others.  But, such is life I suppose!


·       Black Mountain (from the south) with dark colored meta argillite and phyllite on the left intruded by granite exposed on the right.

The name of Black Mountain comes from the western side where very dark gray to black phyllite and meta-argillite crop out---not basalt as some people in town will tell you. The protolith, that is the original rocks, were sedimentary mudstones, siltstones and shale that were subjected to metamorphic processes like heat and pressure during their long burial and subsequent intrusion by the granitic batholith.  These rocks are Early Proterozoic in age and mapped as Precambrian X (Leighty and others, 1997); however, in the current stratigraphic terminology X refers to rocks of the Paleoproterozoic with ages ranging from about 2.5 Ga to 1.6 Ga.  Again, the Ga refers to billions of years before present.  They dip steeply to the west (probably due to sliding off the granite) and are nicely exposed in outcrops along Cave Creek Road heading into town. 


West dipping metasedimentary rocks near Black Mountain.

The east side of the Mountain exposes coarse-grained granite of Middle Proterozoic age, mapped as Precambrian Y.  Today these rocks would be termed Mesoproterozoic with an age range of approximately 1.6 Ga to 1.0 Ga.  The granite is actually part of a large batholith that extends in the subsurface to the south but reappears in other localities such as the famous Phoenix landmark, Camelback Mountain.
 

Coarse grained Mesoproterozoic granite.
There is a large granite pediment to the east of the Mountain where the rock is easily erodible into grus, that is pebble and pea size hunks of eroded granite. (Leighty and others, 1997).  But, there are some really great hills of rounded granite boulders sticking up through the eroded pediment.

Boulder inselbergs, Mesoproterozoic granite.

I have tromped through the area around Cave Creek and noticed numerous mining “holes,” pits, and tailing piles; however, the early prospectors were not overly successful.  Apparently they were looking for gold or copper (some green coatings on rocks) and some areas did give up minerals.  The Phoenix and Maricopa mines directly north of Cave Creek produced about 17,000 ounces of gold, and actually supported a 100 stamp mill and cyanide leaching operation (Wilson, 1934).  On Black Mountain itself the Mormon Girl Mine was a lode gold mine and out near the Cave Creek Campground the Go John Mine was an active lode operation.  I even tried panning for placer gold in some of the stream beds where I could locate a little water after a rain; however, bending over a pan is tough on the ole back when the flakes are absent!   The only evidence of mineralization that I have observed were some outcrops where the Precambrian X rocks are composed of specular hematite.  I don’t believe that area rocks were ever mined for iron.


Entrance to Clay Mine at Cave Creek Regional Park.

I suppose the most successful mine in the area is located west of town in the Cave Creek Regional Park operated by Maricopa County.  A hundred yards or so from the campground is the remnant of the Clay Mine.  As with most early prospectors, the guy (I presume guy) was searching for gold along a clay/talc zone in the dipping Precambrian X rocks.  My initial examination and statement (to myself) was something like “why in the world would he dig here, I see absolutely no indication of mineralization.”  I guess that was a correct assumption in that the mine did not produce gold.  But, it did produce wealth for a later owner by the name of Leila P. Irish.  Ms. Irish decided to mine the clay, mix it with water and then sell the concoction as a miracle elixir, something that would cure any and all ailments. According to the local historians, Ms. Irish became quite wealthy, an innovative snake oil saleswomen.  I tried it out with my own mixture and just about upchucked!  Whatever, it takes to make money, I guess. 

As I reach maturity, days and weeks often fad into obscurity and disappear from the inner recesses of my mind---nature’s way of clearing out the unneeded gigabytes.  However, I easily remember moments: my first teenage kiss, the first time that I viewed my future spouse, the birth of my children (but not their weight and length), the day I left the University, but especially sunsets.  


REFERENCES CITED 


Leighty, R.S., S.J. Shotnicki and P.A.Pearthree, 1997, Geologic Map of the Cave Creek Quadrangle, Maricopa County, Arizona:  Arizona Geological Survey OFR-97-01.

Wilson, E,D., J.B. Cunningham and G.M. Butler, 1934, Arizona Lode Gold Mines and Gold Mining:   Arizona Bureau of Mines Bulletin 137.
       
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