It’s not my Fault

This post finds us back in Central Highlands of AZ, but we continue examining batholiths. We are going to take another day trip north of Lake Pleasant (see Day Tripping post). This time we are going to traverse a faulted region with the Tertiary volcanics and a pC granitic batholith, as seen in the geologic map of this area.

The goal of this trip is a back door to Crown King, up the Agua Fria river drainage basin. This route traverses a complex terrain composed of 1.6 GA (billion years ago) granite and metamorphic rocks, and younger volcanics and sediments. This trip is different from the previous posts because the granite (pluton/batholith) is not entire, but has been broken by a number of geologic faults. These breaks in the Earth’s crust are indicated by heavy lines on a geologic map of this area.

The pC granites (xG, colored gray on the map) are differentiated based on the distribution of elements Na (sodium), Ca (calcium), and K (potassium) within the minerals that construct them. The observed variability is astounding, probably because (1) this is a mining area and there have been many detailed geochemical studies; and (2) this is a batholith that represents many pulses of intrusion between 1.5 and 1.8 GA; that is a period of ~300 million years.

This blog isn’t about geology only, however. The ride up all of those faults from <1200 feet to 5800 feet at Crown King is not possible without road building; this brings us to an important concept in offroading. Much of the adventure lies in traversing roads that were built but not maintained. This is one example, as seen in this photo of the switchbacks required to make the climb on unmaintained access trails from Pleasant to Crown King.

The need for access and thus roads in underlined by the evidence of abandoned habitation along the way.

As with other steep climbs, this one also ends in a high-altitude wonderland of pine and deciduous trees and a lake.

To summarize this easy 4×4 day trip; we climbed through Holocene colluvium and river sediments (again) and through a highly faulted and mineralized (mining) zone thru Tertiary volcanics into a pC batholith that is the highest elevation in the region (i.e., Crown KING), where Americans have extracted vast amounts of copper, tin, lead (not much gold) at great effort.

Their efforts (and Mother Natures’) allow us to take this fun day trip today!