Border Hill National Natural Landmark EarthCache
Border Hill National Natural Landmark
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This is a good, if not spectacular, example of wrench faulting, aka buckle. Since such examples are rare, especially outside the Pacific Coast region, this site is nationally significant. It illustrates a fundamental and important geologic process. By turning onto the county road, you get a nice chance to stretch your legs (in the warm season be alert for desert critters).
Both sides of the highway are your public land, managed by the Roswell Field Office, Bureau of Land Management. We at BLM are using the Earthcache as a method of public interpretation for this very interesting and unique geological structure. As you approach the cut, slow down and get ready to turn north onto County Road EO34. At the Earthcache location, turn your vehicle around, facing the cut and get out and walk about 100 feet so you have a good safe and unobstructed view of the cut. Note the wrench to your right front. The rock matrix is known as breccia. the wrench fault is much more dramatic a feature than the more mundane process the limestone is undergoing. It's like pushing a carpet up against a wall and thus getting a series of buckles.
When you pass mile posts 307 and 308, and geocache GC1AVKC, note the bedding in the cuts - these are also buckle-related features.
Two get credit for your visit, it's test time - please email me the answers for at least 2 of the following questions (remember - do not log your answers - but email me - and I'll let you know how well you "studied"):
1. How many miles long is the Border Hill wrench fault?
2. Who first recognized this geological feature in 1920?
3. What are the names of the other wrench faults between Border Hill and Roswell?
4. The VERY interesting feature at the Lincoln-Chaves county line - why do you suppose it's not closer to Border Hill? (make sure to stop at geocache GC17CB2).
Extra Credit
1. What's the name of the buckle/wrench at mile post 326?
2. What is the name of this surface limestone formation around here and what is the general 5-letter German word to describe such soluble rock throughout this region? (answer requires a little more research beyond this page (hint, cave-related).
The Border Hill Structural Zone
Typified by this long ridge and road cut - this is one of several buckles on the Pecos slope, in otherwise gently (eastward) dipping Permian strata. It is the most strongly deformed of the group. It represents a long, narrow, deformed zone, 96 kilometers (60 miles) long, somewhat less than 1.6 kilometers (1 mile) wide at its widest, but with the zone of relatively steep dips ranging from 152 meters (500 feet) to 488 meters (1,600 feet) in width, produced by wrenching (right strike slip) and appearing in surface expression as an anticline or fault or both. The buckled-up structures produce a line of hills 60 meters (200 feet) to 90 meters (300 feet) above the adjacent plain. Breccia has been formed in the fault zone and may readily be seen in the road cut where U.S. 70/380 cross the structure 39 kilometers (24 miles) west of Roswell.
Topographically, the buckles are represented by northeast-southwest trending ridges above the plains. Border Hill is the largest, most prominent; others are known as Y-O, 6-Mile and Serrano. 6-Mile is somewhat prominent and it is quite wide. Border Hill was recognized by Merritt in 1920 and has since been studied by many investigators.
References
Gross, Gerardo Wolfgang; Roberta N. Hoy; Christopher J. Duffy, November 1976, Application of Environmental Tritium in the Measurement of Recharge and Aquifer Parameters in a Semi-Arid Limestone Terrain, Technical Completion Report, Project No. B-041-NMEX, New Mexico Water Resources Research Institute, in cooperation with Department of Geoscience, New Mexico Institute of Mining and Technology - (visit link)
Merritt, J.W., 1920, Structures of Western Chaves County, New Mexico: Amer. Assoc. Petroleum Geologist Bulletin, v. 4, pp53-57.
Kelley, V.C., 1971, Geology of the Pecos Country, Southeastern New Mexico: New Mexico State Bureau of Mines and Mineral Resources Mem. 24, 75 p.
Additional Hints
(Decrypt)
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