The four corners area lies entirely on the Colorado Plateau, and is made up of an array of geologic features including gentle uplifts, monoclines, broad basins,diatremes, and laccolith ranges (Baars, 1995 ).
The geologic setting of Navajo Country is made up of the Chuska Mountains and Defiance Uplift that separate the San Juan Basin and the Black Mesa-Holbrook Basin. The San Juan Basin is bounded on the east by monoclines and underlying basement faults of the Chama and Nacimiento-San Pedro Mountains, on the south by the Zuni Uplift, on the west by the Defiance Uplift, and to the north by the Hogback monocline and La Plata Mountains. West of the Defiance Uplift is the Black Mesa-Holbrook Basin complex, bounded on the south by the faulted escarpment of the Mogollon Rim, to the west by the Echo Cliffs and East Kaibab monoclines and to the north by the Comb Ridge monocline of the Monument Upwarp (Baars, 1995 ).
The geologic history of the four corners area goes back more than 1.8 billion years. Precambrian basement rock is made up of mostly metamorphic rock with some igneous rock and underlies younger unmetamorphosed sedimentary rock. Paleozoic rocks are composed of thick layers of limestone, sandstone, siltstone, and shale that accumulated in shallow continental tropical seas. Mesozoic rocks were formed mostly by terrestrial deposits and are mainly sandstones with some shale. Cenozoic rocks include igneous intrusions, diatremes and terrace gravels, monocline:
A local steepening in an otherwise uniform gentle dip. diatreme:
A breccia-filled volcanic pipe that was formed by a gaseous explosion.,laccolith:
A concordant igneous intrusion that has domed the overlying rocks and has a known or assumed flat floor and a postulated dikelike feeder beneath its thickest point. It is roughly circular in plan, less than five miles in diameter, and from a few feet to several hundred feet in thickness, escarpment:
A long, more or less continuous cliff or relatively steep slope facing in one general direction, separating two level or gently sloping surfaces, and produced by erosion or faulting., Precambrian:
Weather-eroded arches begin their formation as deep cracks which penetrate into a sandstone layer. Erosion occurring within the cracks wears away exposed rock layers and enlarges the surface cracks isolating narrow sandstone walls which are called fins. Alternating frosts and thawing cause crumbling and flaking of the porous sandstone and eventually cut through some of the fins. The resulting holes become enlarged to arch proportions by rockfalls and weathering. The arches eventually collapse leaving only buttresses that in time will erode.
All geologic time, and its corresponding rocks, before the beginning of the Paleozoic; it is equivalent to about 90% of geologic time.,Cenozoic: The latest of the four eras into which geologic time is divided; it extends from the close of the Mesozoic era, about 65 million years ago, to the present. This era is sub divided into Tertiary and Quaternary.
Sandstone is composed of very coarse to medium grained sheet sandstone and some mudrock that are on top of the Cuba Mesa formation. The sandstone in this area of Ditch canyon dominates this area.(Baars 1995)
Go to the listed location and find the arch to answer the questions.
Answer the following questions as you take this hike. To receive credit for this cache you must do the following.
1. Look at the soil under the arches and try to determine how these arches were formed?
2.How long do you think these arches will stay up?
3. Which arch will break first and why?
Contacted BLM Farmington Office and they said as long as it is not near private land ok.