New Mexico - South - Potrillo Volcanic Field

The Potrillo Volcanic Field is southwest of Las Cruces in the southern part of New Mexico.  When I have visited the area it has usually been from the west - driving from the Deming area.  There are several areas within the Volcanic Field which are of particular interest.  If you are interested in road videos, watch: Road to Providence Cone (geology and petroglyphs) of this area.  The New Mexico - South Central photo gallery includes photographs from this area.


In late August 2014, my brother, Mike, and I took a trip to Aden Crater in the Potrillo Volcanic Field about 30 miles east of Las Cruces, New Mexico, USA.  The Potrillo Volcanic Field is located in the Rio Grande Rift which extends from central Colorado, down the Rio Grande River, and into northern Chihuahua.

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Aden Crater Potrillo Volcanic Field 25 miles west of Las Cruces New Mexico, USA

Aden Crater is a small shield volcano which was most recently active about 16,000 years ago.  A number of lava tubes are associated with the crater and deep vents are reported at this location.  Jerry Hoffer posits that the current geologic feature started as a series of lava flows from one vent, building a shield cone over time.  That activity was followed by more explosive eruptions which cast volcanic material outward forming a roughly circular rim around the vent.  The formation of the rim was followed by more lava flows which were contained within the rim.  The lava tubes, in the lava field within the walls of the crater, are collapsing and the areas along the rim are badly fractured (photo below).  As is often the case when the pressure beneath the surface ceases, the lava drained back into underground vents, and eventually the area above the vent collapsed, forming a large pit in the southeast corner of the crater.  The west wall of this pit is pictured below the following photo.

Aden Crater Potrillo Volcanic Field 25 miles west of Las Cruces New Mexico, USA
Aden Crater Potrillo Volcanic Field 25 miles west of Las Cruces New Mexico, USA

The areas through which we walked to get to the crater, and the crater itself, were covered in grass and wildflowers; in addition to the cholla, yucca, ocotillo, and other plants that we expected.  Everything was green, the plants were responding to our recent rains.  The photograph below was taken from the top of a small dome in the crater.  It is a view of the interior of the crater (looking south).  The crater floor is covered with grass and is bounded by the rim of the crater (dark mounds just below the skyline).

Aden Crater Potrillo Volcanic Field 25 miles west of Las Cruces New Mexico, USA

The crater is within a Wilderness Study Area.  Vehicles are prohibited within such areas (we noted, however, that some people had illegally driven their vehicles into the crater).  We parked at the road (upper left of image to the right) and  walked south toward an obvious lava cliff on the north wall of the crater (see photo at the top of the blog).  The walk was across a lava field which was broken and shattered in places and smooth in others.  There were small lava tubes along the way.  We entered the crater area just west of the lava cliff mentioned above.

Directions:  Take exit 116 on I-10 between Deming and Las Cruces.  Travel east for two miles on Frontage Road 1028.  This road reaches a dead end.  Turn south on a dirt road at this point and travel 7 miles (initially the road heads south but then it intersects a railroad which it follows east on the north side of the railroad right-of-way).  At this point, cross the railroad, and continue east on the County Roads which are parallel (and adjacent) to the railroad.  At 14.2 miles from the end of the Frontage Road or 7.2 miles from the railroad crossing, turn south on a “one-lane track”.  Travel about four miles, the crater is visible for quite some time so where you begin your walk is dependent on parking along the road and your own desires.  There are no marked trails.  Our walk into the crater was roughly 4,000 feet each way.  


Guzman Lookout Mountain is located a couple miles north of the U.S. - Mexico border on the western edge of Dona Ana County.  The mountain is a 519 foot high cinder cone, reaching an elevation of 4,619 feet.  Cinder cones are the most common geologic feature in the West Potrillo Mountains.  As you can see in the photographs below the southeastern portion of the mountain has been quarried for scoria.  Scoria, is a volcanic rock which is porous like pumice but slightly heavier, it does not float.  It has a high strength to weight ratio and is, therefore, used in many construction applications.  It is also used in landscaping.  The deposit of scoria at Guzman Lookout Mountain consists of well sorted cinder and is about 350 feet thick.

Guzman Volcano Potrillo Volcanic Field New Mexico

The rock mined here was transported by truck south on County Road A002 to the town of Malpais, which was a water stop on the El Paso & Southwestern Railroad.  It was also the point from which the rock was transported to other parts of the rail line where it was used as ballast for the bed of the railroad.  All that remains of Malpais are a few foundations and assorted debris.

Guzman Volcano Potrillo Volcanic Field New Mexico

This section of railroad line was completed in November of 1902 and abandoned on December 20, 1961.  When the railroad operated, trains passing through Malpais at 3:30 p.m. would arrive in El Paso at 5:10 p.m. (West bound: leave El Paso at 8:30 a.m. and pass through Malpais at 10:01 a.m.), taking one hour and forty minutes to cover the 49.1 miles between the two points.  Sleeping cars were available on some of the trains running between El Paso and Douglas, Arizona.


On Saturday (September 6, 2014), my brother, Mike, and I returned to the Potrillo volcanic field south of Interstate-10 between Las Cruces and Deming, New Mexico.  Our point of entry for this trip was New Mexico State Road 9.  In the map to the right, the US-Mexico border is at the bottom of the image, the starting point is at the red marker (NM-9).  From NM-9 we traveled north on County Road-008 (also signed as CR-08 and CR-008).  Roughly 3/4 of the way in we took a sharp turn to the right (east) on CR-14 (or CR-014).  After a short distance we turned north again and stopped at Hunt’s Hole.  After our stop we traveled around the western rim of Hunt’s Hole on A-013.  At the “intersection” of A-013 and A-011 it is possible to travel northwest a bit to Kilbourne Hole (the end of this trip indicated by the green marker).  The small mountain range to the west of the route are the East Potrillo Mountains which are an example of “rift-flank uplift” along the western edge of the Rio Grande Rift.  We were unable to leave the area via A-013 (a public county road) because it was blocked by a locked gate placed by “Joe’s Ranch” owned by Joe Delk, creating a substantial hardship for travelers and potentially a dangerous public safety issue.  The roads are dirt and, because of recent rains, mud was very deep in places.

We also visited Phillip’s Hole, which is east of Hunt’s Hole.  Phillip’s Hole and the Potrillo Maar (located roughly at the intersection of NM-9 and CR-008) are larger and have less defined features.  Often they are not depicted on maps.

These three “Holes” are maar volcanic craters.  A maar volcano is created by a steam explosion.  Magma super heats water in the ground which is contained (in this case by a lava flow).  At some point the pressure is so intense that the steam explodes upwards.  Typically this does not create a volcanic cone but the expelled material and the void left by the steam build up causes the surface to collapse creating a “hole”.  In the case of Kilbourne Hole, roughly 500 million cubic yards of material were ejected by the explosion.  The age of these maar volcanos is thought to be between 24,000 and 80,000 BP.  

All three holes are roughly circular in shape.  Kilbourne Hole is about a mile wide (E-W) and two miles long (S-N) and roughly 300’ deep.  Basalt and pre-sandstone (composed of volcanic ash) cliffs make up the boundaries of Kilbourne and Hunt’s Holes.  The photo to the (upper) right shows the cross-bedded volcanic surge material (“sandstone” cap) which covers the Camp Rice Formation (reddish material deposited by a south flowing river which emptied into a playa near El Paso) along the southeast rim of Kilbourne Hole.

Kilbourne Hole Potrillo Volcanic Field West of Las Cruces New Mexico, USA

Basalt cliffs form the rim of most of Kilbourne Hole.  This layer of basalt is what remains of the cap which contained the super heated steam prior to the explosion (photo below).

Kilbourne Hole Potrillo Volcanic Field West of Las Cruces New Mexico, USA

Hunt's Hole Potrillo Volcanic Field West of Las Cruces New Mexico, USA

The cross-bedded volcanic surge material at Hunt’s Hole (photo above) is similar to the strata at Kilbourne Hole.  At Hunt’s Hole the unconformity between the volcanic surge material and the Camp Rice Formation is dramatically displayed in places (photo below).

Hunt's Hole Potrillo Volcanic Field West of Las Cruces New Mexico, USA

Both Kilbourne Hole and Hunt’s Hole are situated along the Fitzgerald Fault.  The Robledo Fault runs along the east side of the East Potrillo Mountains.


A few weeks ago (September 6, 2014) I saw a Common Green Darner, Anax junius, at Hunt's Windmill in Phillip's Hole (Potrillo Volcanic Field, West of Las Cruces, New Mexico, USA). The Common Green Darner is one of the most common North American dragonflies.  Like dragonflies generally this species feeds on small insects, including other darners and butterflies.  References note that this species perches lower than many other darners and given the vegetation where we found it, that is true by definition.  The copulating pair shown here was perched on grass protruding from a pool of water which had seeped out of a water trough.  

Anax junius  -  Common Green Darner

© Robert Barnes 2017