A Treasure of Scenery Found: Lost Mine Trail

My brother, Randy, maintains that Lost Mine Trail gives you the most "bang for the buck" in terms of scenery versus effort expended, and, after taking the hike myself, I can't argue with him. The trail begins in Green Gulch in the high Chisos Mountains at a well-marked trailhead and is relatively effortless until you get toward the end, where you do have to expend a bit of effort in elevation gain. However, all along the way you are offered dramatic views of the Chisos Mountains.

You can look down two canyons as you get toward the end of the trail. The view below, looking east, is of Pine Canyon, which cuts through the heart of the Pine Canyon Caldera, a small caldera, that erupted around 33 million years ago. (A caldera is formed when lava exits a volcanic mountain, removing the means of the mountain's support. The mountain collapses, resulting in an eruption of pyroclastic volcanism.) The result of this eruption was the deposition of glowing clouds of ash and debris called ignimbrite, forming the Pine Canyon Rhyolite, formerly known as the Brown Rhyolite. (The nomenclature of the rock units in the Chisos Mountains has undergone a recent change to correspond to the latest research. Some units with the same name and similar properties and age in different parts of the park have been shown not to be the same units.) Rhyolite is a volcanic rock very high in silicon and oxygen and whose deposition tends to be accompanied by violent eruptions due to the high viscosity of the rhyolitic magma, which can trap volcanic gases until the pressure builds up to explosive proportions.

Figure 1

Along the trail you come across the volcanics of the Chisos Group of rocks (formerly known as the Chisos Formation). The image below is of a layer of Chisos volcanic ash along the side of the trail. The Chisos Group was deposited in various eruptions and sedimentary episodes beginning around 47 million years ago, prior to the Pine Canyon Caldera eruptions.

Figure 2

The Agave americana (century plants) were gorgeous along the trail. Below, my brother, Randy, is taking a picture of a particularly nice specimen with beautiful Juniper Canyon in the background. The higher ridges on the right are composed of the rhyolitic Boot Rock Member of the South Rim Formation (formerly, the Lost Mine Rhyolite). The lower ridges mark the outcrop of an igneous intrusion, a body of magma that pushed its way upward into the surrounding rock.

Figure 3

Here is the picture Randy took. The blooming Agave on this hike were spectacular. It could be that the exceptionally rainy spring attributed to their beauty (but I'm no botanist).

Figure 4

The following picture is a view toward Casa Grande Peak, which is topped by the very resistant Emory Peak Rhyolite, formerly known as the Burro Mesa Rhyolite. (The rhyolite on Burro Mesa has different origin.) My brother, Randy, formerly known as Alan, pauses to take in the view. (Actually, Randy did not have to change his name to suite the new nomenclature. However, in another sense this is true. In England "randy" has a bit of a vulgar meaning, so when we visited him there we would always refer to him by his first name, Alan, in public.)

The Emory Peak Rhyolite also forms the "caprock" on Emory and Lost Mine Peaks. Emory Peak is the highest point in the park at 7835 feet elevation. To the left of Casa Grande is the northern shoulder of Toll Mountain, on top of which is found the Boot Rock Member. Stratigraphically, the Emory Peak Rhyolite lies on top of the Boot Rock Member which, in turn, overlies the Pine Canyon Rhyolite. All these are members of the South Rim Formation, which was erupted between 33 and 32 million years ago. Note the Agave just beyond Randy and the Sotol to his right, both with tall blooms.

Figure 5

Juniper Canyon was particulary gorgeous this trip (June, 2007) due to the wet spring. Canyons such as this widen as mass wasting, processes (for example, rock falls and soil creep) erode away the slopes. The debris from these processes are moved downstream during the infrequent desert downbursts, deepening the canyon.

Figure 6

Below is a view back toward The Basin. Casa Grande is on the left. In the distance is The Window, a gap between Amon Carter Peak on the left and Vernon Bailey Peak on the right. The Window is the only outlet for water from The Basin.

Figure 7

In this view of Juniper Canyon you see a linear igneous intrusion associated with the formation of the Pine Canyon Caldera. It is continued on the other side of the canyon where it forms Hayes Ridge. Boot Canyon descends into Juniper Canyon between this intrusion and the cliffs in the right middle distance.

Figure 8

This is the end of the trail. It terminates at an east-west trending igneous dike, a sheet-shaped igneous intrusion that cuts across pre-existing geologic structure. Here you see brother Randolph with his back on the dike and his feet on what was previously known as the Wasp Spring Flow Breccia (now a unit of the Boot Rock Member of the South Rim Formation). The steep dropoff behind him is apparently the result of a north-south trending fault. Faults are often zones of weakness in the rock where erosion can be enhanced. As indicated in the image, Lost Mine Peak is to the left and Crown Mountain is in the distance. The higher elevations of Crown Mountain consist of the Boot Rock Member (formerly the Wasp Spring Flow Breccia overlain by the Lost Mine Rhyolite). The flatiron below Crown Mountain appears to be made of Pine Canyon Rhyolite, the original material erupted from the Pine Canyon caldera mentioned above.

Figure 9

Lost Mine Peak. Legends of a lost mine on the peak are almost certainly fabrications. Note the grayish rock extending from lower right to upper left across the face of the mountain. This appears to be another igneous dike.

Figure 10

A closeup of the contact between the "Wasp Spring Flow Breccia" and the dike at the end of the Lost Mine trail. The fault scarp with a shear dropoff is on the other side of the backpack.

Figure 11

In this view you are looking almost due south. Elephant Tusk and Backbone Ridge (just to the right of Elephant Tusk, on the edge of the image) are in the distance, almost eight miles away. Both are igneous intrusions. The fault at the end of the trail is marked with the dashed line, and Lost Mine Peak is off to the left. The Rio Grande, about 5000 feet in elevation below you and 18 miles distant, is the greenish strip indicated. At this point the Rio has turned northward as it rounds its Big Bend. The rocks in the foreground on the lower right may have been distorted to their current positions by action along the fault.

Figure 12

Finally, here is the intrepid explorer viewing the horizon for new lands to conquer. My wife has dubbed this picture "Nerd of the Jungle" and has gleefully sent it to all her relatives.

Nerd, Nerd, Nerd of the jungle,
Mounts the rock with pep.
Nerd, Nerd, Nerd of the jungle,
Look out where you step!

Figure 13

FORWARD to the Chimneys

BACKWARD to Rancherias Canyon

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