Essays
Moseying: Locations of Interest
The Sierra Madera Astroblem
February 9, 2005
Have you been to the Sierra Madera Astroblem? It is the best example of an astroblem in the United States! If you have gone to the Big Bend National Park using the road between Fort Stockton and Marathon on U.S. 385, you crossed it ten miles south of Ft. Stockton. An astroblem is a feature caused by a meteor with enough force to blast rocks outward, as well as leaving a crater. Many astroblems have a central conical peak that looks like a volcano. The Odessa Meteor Crater is a small feature, but the Sierra Madera Astroblem is eight miles across. Sierra Madera, the peak in the center, rises 600 feet above its surroundings. The peak is four miles in diameter.
When I was returning from giving a speech in Alpine in October, I took the long way home, first going to Marathon instead of going directly to Fort Stockton. I had to stop and check out the bookstore in Marathon, and stop at the Warnock Reststop in the Glass Mountains just for old times sake. Roland Warnock, the father of the late Dr. Barton Warnock (the premier botanist of the Trans-Pecos) worked for the highway department for years. Barton’s nephew, Kirby Warnock, published Roland’s memoirs, “Texas Cowboy,” a wonderful description of life in west Texas starting in 1919. I always stop at the rest stop and get out and walk around, looking at the vegetation and birds, and the pretty view of the valley to the south.
On the way north I stopped on Six-shooter Draw. To my surprise there was a good-sized puddle of water not far from the low water crossing. I could see the peak within the astroblem (on private property) reflected in the puddle. I looked longingly up at the peak, wishing I could go hike around. It is composed of Permian limestone that was originally over 4,000 feet below ground. The crater itself may have been over a mile deep after the meteor struck over 60 million years ago, but over time it has mostly filled with alluvium (material washed in by rain.) The walls of the crater are no longer sheer as in the Arizona Meteor Crater near Flagstaff, but are now a very gentle slope of no more than a hundred feet of change of elevation.
Scientists involved in planning lunar exploration extensively studied the Sierra Madera Astroblem in the 1960s. It was determined that studying the rocks in the central uplifts of astroblems one could determined the rock structure deep into the subsurface. In recent times Fort Stockton has had a private concern become interested in developing a “spaceport” where rockets bound for the moon and beyond, someday. High school students at Fort Stockton design rockets for a competition intended to encourage the students to become interested in engineering careers. Did knowledge of the Astroblem lead to the idea of the spaceport? Diaries of the soldiers posted at Fort Stockton during the 1870 call the region desolate, vermin-infested, and as having unbearable heat. What a difference in perceptions of the place – spaceport versus useless desert!
My paleontologist father was the first to tell me about the Astroblem – in fact, every time we passed it, he would bring it up! He studied foraminifera to date rocks and determine formations for the oil industry. Oil is trapped by deformation in rock structures – and the Astroblem is a wonderland of “folds and faults.” In the 1980s he “did the paleo” for a company exploring the Astroblem. It was one of those “hush-hush” jobs. The geologist “sitting on the well” would drive to Midland and deliver the samples to my father’s door at odd hours.
Because of the age of the crater and its ensuing refilling, the feature is not readily noticeable as a meteor crater. Many people drive through it totally unaware of its significance. Don McGookey, author of “Geologic Wonders of West Texas” believes that the Astroblem should become a state park or a national monument because of its geologic significance. Much of the Trans-Pecos region has a volcanic geologic history formed by massive lava flows that emerged from far below the earth’s surface, although there were classic volcanos erupting. The nearby Glass Mountains have areas of limestone like the Sierra Madera Astroblem.
Different parent rocks form different types of soil, which means the plant life and its corresponding faunal life has a number of differences. Years ago, I was lucky enough to accompany Dr. Barton Warnock on a field trip into the Glass Mountains in Hess Canyon. One of the “eye-openers” of his talk discussed places where volcanic rocks were next to limestone rocks, which meant that there were significant differences in the plant life within just a few hundred feet. For example, in limestone he showed us small clumps of Desert Orange and Tickbush in the canyon. The nearest population of those species is in the Guadalupe Mountains, over 200 miles away. In a crevice of igneous rocks not far away he pointed out a white agastache only found in that type of soil.
He also showed us populations of endemic species of plants found only in the Glass Mountains. Since then, I have wondered if those species, Roberts’ stonecrop and the Glass Mountains rock daisy, are also to be found on the peak of the Sierra Madera Astroblem. Over the years Dr. Warnock received permission to explore most of the ranch country of the Trans-Pecos, but I do not know if he ever surveyed the Sierra Madera Astroblem.
As I was working on this story a visitor (after asking what I was working on) mentioned that he had been there, and that the Elsinore Ranch had owned it for a hundred years. The latest information (1998) I found online reported that it is now known as the Escalera Ranch (since its brand is a ladder), owned by Gerald Lyda, who bought it in 1992 from Douglas Giddings. Giddings’ grandfather Edwin bought the ranch in 1884 from the GC&SF Railroad, which was given the property in exchange for money and materials to build the Texas state capitol building.
As one approaches the peak in the center of the crater, the highway crosses over Six-shooter Draw. I checked The Texas Handbook Online, which reported the name of the draw came from the cattle brand of an early day ranch in the area. Looking for more information, I dug around in the library of the Sibley Center, and in Olan George’s “Round-up of Memories” about Pecos County and Fort Stockton, I found a different story. As an employee of the county, George had parked on the highway (then a dirt road with no bridges) after a big rain, and when two or three cars had arrived, would chain them together and drag them across the slushy mud of the draw with a tractor.
Later he asked Judge O.W. Williams of Fort Stockton (who recorded many wonderful stories of the region) how the draw got its name. The Judge said a sheepman was slowly drifting 3000 head of sheep across the country. The local cattle ranchers became irritated with his slow pace and paid him a visit. After the cattlemen told him if he did not leave they would scatter his sheep, the sheepman packed up in a hurry and left. Afterwards the sheepman noticed his six-gun was not with his gear and figured the cattlemen had slipped into camp before their “official” visit and stolen it while he was gone. Two years later, the sheepman returned and again camped in the same spot. He walked over to the mesquite tree where he had laid his suggans (bedroll) two years before, and there was the gun.
The Astroblem is like the sheepman’s gun – unseen, but in plain view.