Friday, February 25, 2011

HIKING PICACHO PEAK

PICACHO PEAK (FAR LEFT).

I currently am camped at Picacho Peak State Park, north of Tucson about 30 miles, and south of Casa Grande about 20 miles.  It is one beauty of a place to spend some time if isolation is of interest.  Although the park is adjacent to Interstate 10, I can sit in my lawn chair and watch the sun go down over mountain ranges perhaps 40 miles away.  It seems that the only “things” between my chair and the mountains are hundreds of saguaro cacti.

Picacho Peak is sort of a misnomer since Picacho is a Spanish word for “big peak” so a translation would be big peak peak.  Whatever the case, it is a fantastic place to camp and hike.  The Park is in the Basin and Range Physiographic Province so most of the many mountain ranges that I see from my easy chair are horsts (uplifted blocks) separated by expansive grabens or half-grabens (down-dropped blocks).  The grabens are now large alluvial basins.  Periodically there are outcrops of volcanic rocks (see previous blog on Ragged Top).

The Park’s main attraction is Picacho Peak, a large chunk of basalt that has been tilted and faulted.  In fact, much of the basalt flow(s) is now hidden under the alluvial fill.  It is my understanding that the volcanics at the Park are about 22 Ma and represent the top plate of a large detachment fault (large normal fault) with the bottom plate being the Precambrian granite and gneiss east across the Interstate—the Picacho Mountains (Kresan, 1987).  I located several instances of old mining structures, mostly glory holes and simple excavations.  The miners evidently were after copper since most of the mines seem to follow greenish-blue stained rock; breccias associated with faults also were common targets. The detachment provided a conduit for hydrothermal fluids that charged the upper-plate rocks with mineralizing fluids that carried Zr and Ba, along with Au, Ag, and Cu, during detachment 17–18 Ma (Brooks, 1986).

As an avid hiker I decided to take my afternoon stroll to the top of Picacho Peak situated at 3374 feet with an elevation gain of approximately 1500 feet in 2.1 miles.  Little did I know that my walk would turn into “a really, really, hard hike”.  The first 900 feet of elevation gain was OK and got me to a saddle, and then I saw something on the other side that made my heart go pitter-patter a little faster.  I needed to go back down before going up again (always a bad sign) and the path down was between two cables, and steep, very steep!  That was only the beginning for the remainder of the hike was always in sight of cables with some climbs 70 degrees.  In another place I had to hold the cables and wiggle up a crack in the basalt—climbs like that are hard on an old guy.  And speaking of age, one of the high school kids sort of hiking with me (I was explaining geology—never miss a chance for that) asked, “Say, how old are you?  You hike pretty good for an old guy”.  The hike ended up about four hours in length with a net gain of 2366 (not 1500) feet in the 2.1 miles.  Old guys rock!
REFERENCES CITED
Brooks, W. E., 1986, Distribution of Anomalously High K2O Volcanic Rocks in Arizona: Metasomatism at the Picacho Peak Detachment Fault: Geology, v. 14, no.4.
Kresan, P. L., 1987, Arizona Geology: An Aerial Tour: Arizona Bureau of Geology and Mineral Technology Fieldnotes, V. 17, No. 3.

mike
THE NEED TO WIGGLE UP A CRACK!

A FAIRLY STEEP SLIDE.


A NETWORK OF CABLES LEADING UP (AND DOWN).
MADE IT TO THE TOP. PICACHO MTNS. IN BACKGROUND.

A VIEW FROM THE EASY CHAIR.



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