This route is an off-trail journey in the Potrillo Volcanic Field (potrillo is Spanish for “foal”) within the northern reaches of the Chihuahuan Desert. Eruption risk is minimal, but there are risks due to temperature extremes, steep and difficult footing, the lack of any trails, the near-total absence of other visitors, and potential navigational hazards such as dust or thunder storms. All of which is made manageable by hiking in the cool season, bringing friends, carrying the requisite navigational aids and keeping an eye on the weather. You get a great hike in stark, other-worldly terrain that is an easy drive from Las Cruces.
Mt Riley is part of a ridge that extends for two miles west to east. For ease of reference it is called the Riley Ridge in this guide. Mount Riley proper, at 5905 feet, anchors the east end of Riley Ridge. “Point 5782” (named after the altitude label on the USGS quadrangle) anchors the west end. South of Point 5782 is the summit of Cox Peak. In this scramble you will traverse the Riley Ridge and return via the Cox-Riley valley.
- From University Avenue in Las Cruces, enter I-25 going south.
- After 3.0 miles I-25 merges with I-10 going east.
- After 29.1 miles (having crossed into Texas) take Exit 8 for Texas Highway 178, also known as Aircraft Road. The exit will first merge onto a frontage road called South Desert Road.
- After 0.6 miles on South Desert Road, at a traffic light, go right onto Texas Highway 178.
- After 2.9 miles, at the state border, the road is renamed to NM 136 (also known as the Peter V. Domenici Highway). Reset your mileage meter here.
- After 6.1 miles on NM 136 turn right onto NM 9. There is a small road sign, but there is no traffic light (this may seem odd as there are traffic lights at earlier junctions on NM 136). If you miss this turn then you will come to the Santa Teresa Port of Entry border station in less than 2 miles.
- After 23.8 more miles, go right onto County Road Ao05. There is the usual road sign as well as a second sign saying “Mt Riley”. CR-Ao05 is a gravel road.
- After 8.5 miles turn right onto a jeep track and park on the grassy area to the side. The jeep track can be a little hard to identify so the following navigation clues may be useful
- After 1.2 miles on CR-Ao05 come to the Mt Riley Ranch, where there are two gates across the road. You will have to open the gates, drive through, close and re-latch them (unless the ranch has left them open).
- After 4.5 miles on CR-Ao05 come to an intersection where County Road Ao07 departs to your right. (CR Ao07 is used for the Cox Peak trailhead, but here it is just used to check navigation).
- After 8.0 miles on CR-Ao05 (approximately) the mesquite and chaparral bushes that line the sides of the road start falling away, and there are larger and larger stretches of grassland beside the road. You can see into the valley between Cox Peak and Riley Ridge. You are getting close.
- After 8.5 miles on CR-Ao05, while crossing a broad and only barely noticeable height of land, you will find a shallow, two-foot wide waterway coming in on your right. Although it doesn’t look much like a jeep track, that’s what it is.
If you go past the jeep track then CR-Ao05 will take on a slight downhill pitch. Turn back. Drivers of low clearance vehicles will want to park immediately beside CR-Ao05. Drivers of high clearance vehicles can drive a mile further on the jeep track to the campsite described below.
The trailhead is just a grassy spot beside CR Ao05. There are no services. When pulling off the road watch for the small mesquite bushes hidden in the grasses. Their thorns are not good for your tire’s sidewalls. Also, if a road grader has recently passed this spot then there may be a small berm on the roadside. High-suspended vehicles would have no problem, but sedan drivers may want to have a shovel handy.
- Starting Elevation: 4440 feet
- Ending Elevation: 5905 feet
- Elevation Gain: 1465 feet
- Distance: 6.1 miles round trip
- Maps: USGS Mt Riley quadrangle
Follow the jeep track as it makes a shallow climb to the east along the Cox/Riley valley floor. This valley is saddle-shaped rather than spoon-shaped. That is, the high point for a traveler going west to east along the valley floor would be the low point for a traveler going south-to-north from Cox Peak to Point 5782. Study that saddle point as you ascend the jeep track. It is important to navigation on return. After one mile on the track come to a campsite with a rock fire ring. Look closely and you will find a much fainter jeep track ascending for another two-tenths of a mile on the Mt Cox side of the valley. The faint jeep track ends at a second campsite. Peruse the prominent rib that descends from Point 5728 almost straight at you. That rib is your path to the ridge. Descend north-east to the central arroyo in the valley floor, cross, and ascend along side a feeder arroyo that takes you toward the rib.
After leaving the jeep track you will be entirely off trail. As you cross the valley floor watch for dense accumulations of prickly pear cactus, thorny mesquite and saw-like sotol. This is no place for sneakers or shorts. At about 1.4 miles from the trailhead the terrain begins to steepen. Leave the feeder arroyo and stick to the rib as it becomes increasingly steep. Initially the rib is rather broad and open, making it easy to throw in a few switchbacks. At about 1.7 miles from the trailhead come to a shoulder on the rib. The gradient eases and the rib-top becomes more sharply defined. Ocotillo plants appear, but oddly they don’t seem to grow well on the very top of the rib (perhaps due to wind-damage). An open ridge-top avenue takes you skyward. The terrain rises and shelves several times, but you eventually arrive at the summit of Point 5782 having walked 2 miles from the trailhead.
The views are terrific. The blocky mass of Cox Peak dominates the south. Immediately to the west are the cinder cones of the Potrillo Volcanic Field. Beyond lie the Florida Mountains. To the north are the Las Uvas and Robledo Mountains, while the Organ Mountains dominate the north-east. Eventually, however, you must turn your attention south of east and focus on the long ridge that will take you to Mt Riley. Descend on easy terrain to reach a pleasant col and then gird yourself for the climb to the first of three peaklets along Riley Ridge. The climb is easy. At the top you get your first view of the middle peaklet, which is topped with a pair of small knolls separated by a little pass. Drop down on steep terrain with lots of loose rocks, cross a minor saddle and rise to “Middle Peaklet Pass” 2.4 miles from the trailhead.
From here look down to the eastern-most peaklet and beyond to the steep flank of Mt Riley. You will definitely be losing lots of hard-won elevation. But, there is much to be learned here. The top of Mt Riley is almost flat. When you eventually near the top you will be coming to a western shoulder and then strolling east in a park-like environment to the summit. This can be seen, in the photo above, where the top of Mt Riley appears slightly notched. The shoulder is on the left and the summit is on the right of this “notch”. More importantly, the climb from the main saddle directly up the mountain’s steep west face is an unattractive route. Instead, when you leave the main saddle you will want to climb the west face until ascent becomes difficult, then turn right (more southerly) and perform a rising traverse across the mountain to gain the rib that descends from the shoulder. That rib can be seen in the photo as a smooth, light-colored curve descending from the shoulder. It is still steep but the footing is better.
Enough theory? Descend from Middle Peaklet Pass down to the last peaklet of Riley Ridge. This terrain is moderately inclined and etched with cattle trails. As you near the eastern-most peaklet you will pick up an old barbed wire fence. Follow it along the ridge to the main saddle directly below Mt. Riley, having hiked 2.7 miles. Continue following the fence across this grassy saddle onto Mount Riley’s west face. Where the grasses give over to juniper, barrel cacti and rock turn right and begin that rising traverse across difficult terrain. As pictured above, you will encounter ledges that are flaking off large piles of broad rock shingles. Some of those piles are none-too-stable. There is a marked improvement in the footing when you gain the rib that descends from the mountain’s shoulder.
On the rib turn uphill and zig-zag past ledges, dodge ocotillo thickets and push by more barrel cactus. (On this date these cacti had orderly circles of vividly yellow fruit on display). The angle is pretty severe so don’t be too distracted as views open to the East Potrillo Mountains. At 3.1 miles reach the shoulder and, as promised, an effortless stroll to the summit cairn in less than 100 yards. The views are similar to those from Point 5782, but with spectacular sight lines east to Kilbourne Hole and Aden Crater out in the middle of the Mesilla Basin. Beyond the craters lie the Franklin Mountains.
Also, there are absorbing views west that reveal the full extent of Riley Ridge. That’s quite a scramble you’ve just had. Take a break. Grab a bite to eat. It can be hard to beat an in-season orange consumed in the warm New Mexican sunshine while sitting on a desert peak and studying possible approaches to the East Potrillos. Eventually, though, the lure of the valley below will induce you to hoist your pack. Head south, picking your way past junipers and aiming towards the east slopes of Cox Peak. Descend a broad rib that tumbles through layers of softer rock and then shelves as it strikes the harder stuff.
Near its foot the mountain sends out two claw-like projections. Stay a little to the left (east) to get onto the south-projecting claw and then turn right and contour down to the top of the south-east projecting claw. Having hiked 3.5 miles, you are nearing the valley floor. You want to set a course that will return you to the valley’s saddle point. There are an infinity of choices. On this route, stay high and contour west along the base of the mountain on easily followed animal trails. This will take you across the southern face of Mt Riley to a point below the ridge’s main saddle. Follow a rib descending from main ridge and gradually work your way into the steep-sided arroyo on the rib’s west side. From the far bank aim towards the center of the valley, but try to avoid losing so much elevation that you have a long climb back to the valley’s saddle point.
Continue west, dropping into drainages and fighting up over each far bank to regain the table-land. Some of this table-land is covered with dense, light-brown grass. The grassland looks attractive from a distance. Up close, however, those dense grasses make it hard to see the light brown rocks that lurk beneath. Walking becomes a very slow process. The juniper, cactus and mesquite terrain is actually easier to negotiate. You quickly learn to steer away from the light brown patches in favor of the dark-colored terrain. At about 4.3 miles, come to the valley’s central arroyo and cross it. Above the bank on the Cox Peak side you should find a well-defined trail heading up towards the valley’s saddle point. This is great for tired legs. Continue along the trail to the valley’s saddle point, cross over, and then head down-valley. At 5.0 miles, return to the campsite at the upper end of the faint jeep track. Follow the jeep track back to the trailhead, having hiked 6.1 miles.
♦This is an outstanding cold-season hike. The conditions at the start of November, for example, were perfect. It was cool, a bit windy and overcast. Hikers who are not training for the Death Valley Marathon will want to stay away during the hot months.
♦A second good reason for favoring the winter months is that I saw only two reptiles on this hike. (One lizard, one horned toad). The reports say that the terrain can rattle in warmer weather. See below.
♦Bring friends. This place is so lonely that there are yellow flowers growing in the crown of County Road Ao05 (these flowers look something like tickseed).
♦Bring a map, compass and a GPS device. Bring knowledge of how to use them. On nice days there may be some grumbling about this (“hey, I can see 100 miles from here”). On nice days that turn sour – when rain or dust blows in – you’ll be glad to have independent means for navigating.
♦Bring all the water that you need for rehydration plus an emergency liter or two. On this November day I used about 2.5 liters of water. It was reassuring to have carried four.
♦RayRay, on Summit Post, has a very complete report on scrambling Mt. Riley. He was able to drive the jeep track and then hiked the Cox-Riley valley to get to the base of Mt. Riley. From there he did a direct ascent and returned by the same route. That cuts the round trip distance to 4.4 miles.
♦Greg at Greg’s Running Adventures has a thoughtful post viewing Mount Riley from a runners perspective. It includes a number of great photos, including evidence that the scramble can be rattle-y.
♦There is a YouTube video of Hadley Robinson paragliding near the summit of Mount Riley. The video was made in 2009 so the images are grainy. The video includes shots of the summit and several good views of the East Potrillo Mountains. Still photographs from the event (with a great deal more resolution) can be found here.
♦This hike is located close to the Mexican border. The Federal Government advises caution in this area due to the potential for illegal border crossing activity. They also warn that the road may become impassable during wet weather.