![]() ![]() Most of the rocks on the ground along the highway are rounded cobbles, covered in a thick cortex of caliche. This part of west Texas is a vast, very flat, open plain, and the area is very quite and peaceful, lending itself to contemplation and the study of rocks. Rattlesnakes are also abundant in this area, and a large feral boar crossed the road not far from me while I was shooting pictures. As with nearly every other highway shoulder in the country, highway debris, old fencing remnants, and so forth, make flat tires a reason for modest caution. The shoulders of the highway are wide, however, and we found plenty of room to safely pull off. The surrounding land is private property, and trespassing is not allowed. A few outcrops near the center seem to be a fluvial or alluvial conglomerate, perhaps post-dating the crater. Though the crater is severely eroded, many of the cobbles along the side of the road are comprised of limestone breccia. Hwy 385 nearly bisects the crater from north to south, passing through the annular basin and just to the west of the central uplift. Looking across the crater region from the raised north rim, as in the picture above, one sees a subtle expression of the annular (or ring shaped) basin surrounding the uplifted central rebound peaks. There are also clear road signs marking the rims of the impact crater, coming from both north and south. The range of hills representing the central uplift of the Sierra Madera impact crater is visible from Interstate 10, in Fort Stockton, 21 miles to the north, and is virtually impossible to miss as you approach the crater on Hwy 385. Even having visited several prior large meteorite impact craters, both I and my travelling companion were somewhat awed. From the remnant crater rim, the central uplift looks like a small mountain range, and the far horizon marks the opposite rim of the crater. Other significant evidence: breccia, megabreccia, morphology.Īpproaching the crater from the north, from Fort Stockton, the visitor drives over a couple of ridges that, more-or-less, mark the original crater perimeter, before dropping down into the shallow annular basin, literally meaning ring-shaped basin, which surrounds the central uplift, or rebound peaks, at the center of the impact. Planar deformation features in quartz (Wilshire et al., 1971).Shatter cones (Howard and Offield, 1968).Geological Society of America Bulletin, v. and Offield,T.W., Impact breccias in carbonate rocks, Sierra Madera, Texas. This section, which is included for each crater on this website, is not an exhaustive list of such published evidence, but is meant to demonstrate that appropriate work has been done for each listing. Without such evidence, a geological structure is not a confirmed impact crater. The impact origin of each location listed on this website has been supported by unambiguous diagnostic evidence of hypervelocity impact that has been reported in a scientific (usually peer reviewed) context. The structure is located in west Texas' Pecos County, and is primarily located on private ranch land, but is crossed by Texas Hwy 385. The database also notes that the structure is 100 million years old or less (Cretaceous). The Sierra Madera crater is listed in the PASSC database, hosted at Canada's University of New Brunswick, as a 13 km structure exposed at the surface in sedimentary target rock.
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