Kilbourne Hole

Kilbourne Hole is a maar volcanic crater, located convert|30|mi|km west of the Franklin mountains of El Paso, Texas, in the Potrillo Volcanic Field of Doña Ana County, New Mexico. The hole is a rare example of volcanic action without a mountainous rim. The theory of formation is that a volcanic eruption occurs in the presence of ground waters, beneath the surface of the earth. As the hot lava and magma encounter the waters, a huge bubble of steam is produced, which blows out a large crater; thus, it is not necessary for the lava and magma to build up a mountainous deposit. The crater is thought to be 80,000 years old [pp. 273-281, Cordell, L. (1975) "Combined geophysical studies at Kilbourne Hole maar", New Mexico, "New Mexico Geological Society Guidebook", 26th Field Conference, as recorded in:] , [p. 310, Charles A. Wood and Jürgen Kienle, eds. (1990) "Volcanoes of North America": United States and Canada. Cambridge ISBN 0-521-36469-8] .

The volcanic features around El Paso and vicinity are part of the Rio Grande rift, which extends northward into Colorado.

Description of the crater

*Latitude/Longitudefn|1:fn|2 31.97 N, 106.97 W
*Elevation: 1292 m
*Crater diameter/depth: 2.4x3.4 km/135m

The hole is over a mile wide, and over convert|300|ft|m deep. Two basalt cliffs inside the crater, with the characteristic reddish purple hexagonal columns, occupy the northeast and southeast sides of the crater. The cliffs are about convert|40|ft|m high. Layers of ashfall and crumbling sediment also rise about convert|40|ft|m high, on the south rim of the crater. "This ashfall section will not support your weight, on the south rim"; it is safer to stay on the basalt cliffs and the sand dunes. Sand dunes have collected on the east side of the crater, rising about convert|100|ft|m above the desert floor. A dry lakebed lies on the floor of the crater.

The basalt cliffs resemble the cliffs of the Devils Postpile National Monument near Yosemite National Park, except that they are not as tall.

Rockhounds can pick up Green Olivine stones, which are available at only about 5 places on earth, such as by the Red Sea, and in Arizona.

Lava chunks exist in abundance. The basalt column fragments are each larger than a person.

Hunt's hole lies several miles just south of Kilbourne hole.

Apollo astronauts trained in these craters in 1969. [http://www.desertusa.com/mag06/apr/volcanoes.html Kilbourne Hole: Apollo training site] [http://history.nasa.gov/alsj/ap-geotrips.pdf Geology field exercises for Apollo missions. p.8]

Directions to Kilbourne and Hunt's holes

Because there is new road-building at the southern end of Doña Ana county, the existing published descriptions are out of date. Compiled here is a description gained by interviewing local residents who gave accurate directions, from their own experience:
*Mile 0.0: Head west on Texas 375 from the intersection of Interstate-10 and Texas State Highway, Loop 375 exit (Trans-Mountain Road) toward Canutillo, Texas.
*Mile 1.0: Head north to Texas 20, the main road of Canutillo, until La Mesa road crosses it.
*Mile 1.7: Head west on La Mesa road, crossing the Rio Grande. This road becomes Texas 259 (La Union - Canutillo road).
*Mile 2.6: Texas 259 becomes New Mexico 28 at the state line. Keep heading west.
*Mile 3.0: Follow NM 28 west until it veers north. Head west at the intersection of NM 28 and NM 273 (McNutt Road) This is McNutt Road, the major road of the county, travelling roughly parallel to the course of the Rio Grande. You will be driving through pecan orchards and cotton fields.
*Mile 5.1: Follow McNutt west to La Union, where McNutt veers south. At this turn of McNutt, turn north on Alvarez and follow Alvarez north through La Union.
*Mile 7.9: You will pass the Mercantile road, La Union road on the way through La Union.
*Mile 8.2: Pavement ends on Alvarez at Short St. Continue north on Alvarez, a dirt road. Don't take El Chavo, a gravel road.
*Mile 8.4: Alvarez will continue northward, but a fork westward, labelled County A-20 will head over the sand bluffs which rise convert|50|ft|m above the Rio Grande flood plain. Take A-20 west.
*Mile 10.0: Top of the sand bluff above the Rio Grande.
*Mile 10.4: Water tank on the northeast side of A20
*Mile 11.7: At the top of the rise there is a cattle guard. Keep heading west on this unpaved road.
*Mile 14.8: Follow the graded road to two cattle guards which surround a crossing of the Union-Pacific railroad line, which runs from El Paso through New Mexico and westward. Cross over the first cattle guard, the railroad track, and the second cattle guard.
*Mile 15.1: Immediately after the second cattle guard, take the graded road northwestward. This road runs parallel to the railroad line.
*Mile 15.5: The graded road hits a cattle guard at County Road 014, heading west. Turn west onto Road 014. Kilbourne hole and Hunt's hole are west convert|12|mi|km. Fall and Winter are the best times to visit; rattlesnakes are awake during the Summer. Stay on the graded road. The surface is a hard-pan called "caliche" which stays drivable; apparently the road is maintained for the benefit of the ranchers here.
*Mile 20.3: Cattle guard. Use caution at rises in the road. Even if you were the driving the only car, with a dust trail clearly signalling your position, the dikes of lava in the desert are NOT level. You could roll your car if you drive too rapidly over the lava dikes, which rise convert|5|ft|m from the ordinary desert floor, and possibly hit an oncoming vehicle.
*Mile 25.9: The eastern-most lava dike is convert|3|mi|km from the foot of the crater.
*Mile 26.9: A rise in the land to the north of the road, and a mile from the dike is the eastern lip of the crater. It is a fine walk across the desert to the lip, which is a sand dune which rises convert|100|ft|m above the desert floor.
*Mile 27.4: Alternatively, continue west on Road 014 and take a side road north to the south lip of the crater.
*Mile 27.5: South lip of the crater.

Use caution. You will be completely isolated here. Cell phones are out of range here. Take several liters of water per person. Wear a hat. Tell others of your plans, and give an estimated time of return. 4WD is not necessary, but a high-clearance vehicle is highly recommended. The road leading down into the crater is not safe - the hardpan will collapse under the weight of your vehicle. In an emergency there is a ranch 3-4 miles (approx) to the west. Border Patrol often encountered as well. Do not travel here alone.

To get back to El Paso or Las Cruces, reverse the directions.The cell phones will start working at the sand bluffs next to the Rio Grande.

Maps and aerial photos

Notes

Links

UTEP Potrillo Maar Experiment http://www.geo.utep.edu/pub/miller/pvfweb/ Satellite view of El Paso region, including Kilbourne Hole, illustrates "The Potrillo Volcanic Field Seismic Experiment"