Sierra de Rosario (Sonora, Mexico)


By: Mark Adrian, Richard Carey


Several months ago, while at my friend Richard Carey's house, I had the opportunity to review a collection of 1:250,000 scale maps of northern Sonora, Mexico. I was intrigued by the numerous Sierra (ranges) throughout the Sonoran panhandle. Having climbed and explored in the Cerro Pinacate area before, I had thought this an interesting area. As I casually ogled and perused the map collection, I was ecstatic to discover a very small Sierra located in the depths of what's named the "Desierto de Altar" or "Gran Desierto". This "Gran Desierto" is a virtual sea of sand, generally located about 45 to 80 miles southeast of Yuma, AZ, in Sonora, Mexico. Technically, this is mainland Mexico. Nestled well within this sea of sand is a small, isolated and rugged range named the Sierra de Rosario. Its range highpoint is a mere 562 meters (1,843.4 feet). Further research in the OPS (Obscure Peaks Section) library revealed an interesting report in March, 1916 by (the late) Charles Sheldon. The report included an aerial view of the range. To quote Sheldon : "The Sierra del Rosario is a series of jagged peaks about 10 miles southwest of the southern end of the Tinajas Altas Mountains and 40 miles east of the Colorado River. Surrounded by a belt of sand dunes, the Sierra del Rosario rises nearly perpendicular to the desert floor, with the highest summit reaching an elevation of 1,820 feet. Isolated and without permanent water, the Sierra del Rosario is the most arid mountain range in North America." Now, being an avid desert peak bagger, this pretty much had me seduced and it didn't take much to entice several other OPS devotees. Although Sheldon was more of a wildlife biologist than mountain climber, his journal reports convinced us to go prepared for technical climbing. To quote Sheldon : "I went up the ten feet. The rock was fairly firm. I found that I could go another ten feet. I did so, and went still farther. Each advance caused me to try to go up still farther. Then I could not turn around and had to keep on, almost straight up along a knife edge. I was clinging to a wall of rock with steep, perpendicular slopes falling away on either side. The whole aspect of the mountain was so savage that it required all my courage not to become nervous and make a false step or take hold of a loose rock. While I was clinging to the rock with both hands, not even daring to look down, a vulture soared easily and gracefully overhead, right up along the crest. I had the feeling that if I ever reached the top safely, it would be my last perilous attempt in these mountains, realizing strongly the claims of my dear wife and family. I worked upward, twice feeling that all had ended, yet I reached the top and then lay flat on my back in the broiling sun and closed my eyes to get relief from the strain I had undergone." So, we went equipped with a 9mm (rope), helmets, rock shoes, harnesses and a variety of slings and biners.

Sheldon's report was from 1916, but it was the only information we had on the area. The Mexican 1:50,000 (similar to "our" 15' maps) revealed a dirt road circumnavigating the range with a short spur dead-ending in the sand dunes NE of the range, many miles from pavement (Mexican Hwy 2). I had anticipated a long approach hike through the sand dunes, but this was only speculation. I had spotted several penetrating dirt roads into the Desierto back in November while climbing the highpoint of the nearby Tinajas Altas Mountains in Arizona, but of the three roads I saw from that summit, all seemed to disappear into the sand. So, our plan was to "burn" a day scouting for an acceptable approach drive, then a day for the climb and a day to drive home or if we were lucky enough, bag another nearby Sierra highpoint.

Friday morning, after a leisurely breakfast and several stops in Yuma, we proceeded south on Hwy 95, acquiring Mexican auto insurance just north of the San Luis, AZ border crossing. We crossed the border about 10 AM (PDT) where I was immediately pulled into the Mexican inspection station. After a couple of questions as to my intentions and destination, I caught up with Richard, Gail and Ken on the outskirts of San Luis, MX, on Mexican Hwy 2. Proceeding east along Hwy 2, views across the Desierto became more foreboding. There was sand as far as the eye could see, except for the dual-horned summit of the far off Sierra de Rosario's range highpoint. Continuing eastwards for about an hour out of San Luis, MX, we stopped alongside a dirt road turnoff that headed south towards Rosario. Here, we took several bearings, a GPS reading and then decided it would be expedient to split the caravan and search independently for acceptable access roads. Of course, we were able to stay in contact via radio. Furthermore, judicious exploitation of GPS really helped us determine which roads were viable candidates. Without these "tools" and the correct maps, we may never have found what roads we did since none were shown heading off of Mexican Hwy 2. So, while Richard, Gail and Ken explored the first of several dirt roads, I continued east, passing several more options and finally came upon, unexpectedly, an ad hoc sign written in Spanish (of course) that, as best I could translate, had something to do with a "park" or "biological preserve". Anyway, it was posted beside a good dirt road and headed south. So, radioing my discovery, I perused this road for about eight miles heading due SW, choosing by instinct the "best" spurs. The road was considerably better to this point, but then I stopped because I had clearly entered the margin of some very deep sand. Meanwhile, Richard, Gail and Ken continued to explore several other dirt roads. I had radioed them my UTM/GPS coordinates, so they knew exactly where I was parked and that I was still about seven miles from the peak. I was concerned because the sand was a definite barrier and about the consistency of beach sand. I also noticed that the road bed was full of trash of all sorts. I couldn't imagine what all this garbage was doing out here. But later, Richard concluded the Mexicans had possibly used this garbage to stabilize what road there was through the sand.

Several hours later, after their relentless search for a better approach drive, Richard, Gail and Ken arrived at my location. We assessed the deep sand, for which their tires were better than mine and we decided to continue along the faint path, they would take the lead. Although there was five miles of sustained sand, we all made it through OK and the sand ended exactly on the topo map where it showed the good dirt road spur starting, just to the NE of the range. We confirmed our location with GPS and were startled at the map's accuracy. Better yet, we were at the base of the range, had plowed over an otherwise LONG and arduous approach hike and we were on a good dirt road. What more could you ask for? So, we continued driving south along the eastern perimeter of the range, stopping occasionally to discuss trailhead options and enjoy the rugged scenery and remoteness. Since it was a warm day, I suggested we continue along the southern perimeter and head towards the range's western side so we would be hiking in morning shade. Not only did the road continue around to the west per the map, there was excellent camping options on a flat bench right at the base of the highpoint. Our GPS reading was that the peak was 0.5 miles away and 1,400' of gain from the desert floor. Being late afternoon, we were more than ready for a well-deserved happy hour, an OPS tradition carried over from our "old" DPS days. The sunset across the sea of dunes provided a constantly changing scene of shadows. After a warming campfire and maybe a few-too-many cervezas, we were all to bed by 8 PM.

Gusty winds that evening shook our trucks with regularity and made for a chilly morning. This was quite a contrast to the near-80-degree temperatures of the previous afternoon. Finally, after all the planning and research and anticipation and now anxiety, we were heading off at 7:30 AM. It was obvious the direct route involved sustained 4th and most likely 5th class climbing. Sheldon's descriptions began to ring true. Nevertheless, we decided to take a route heading NE towards a saddle on the main ridgeline. From what we could see this looked no more than class two and proved to be easy. We arrived at the breezy perch about an hour later. From here, we could not see the highpoint, but views to the east and west across the dunes were unique and impressive. It was going to be a great day in the Sonoran desert. Breaking here, we again pondered several route options and made a decision to diagonal S up along the crest. This went well for a few hundred feet, but then cliffed out. So, we had to descend about 75' into a nearby gully full of loose rocks, some well-placed and annoying brush and a few third class moves here and there. Continuing SSW up this gully, we were sure we were headed for the highpoint's summit block. Continuing upwards we topped out at a prominent notch in the ridgeline about 9:30 AM where we faced a 30 foot 4th/5th class pinnacle, or so it was from this notch on its east side. We dropped our packs and discussed our options. After assessing the eastern option, we decided to drop down and around to the pinnacle's west side. So, Ken and I went to scout this out. When we came around the pinnacle's northern edge, we were startled to see two higher peaks to our southwest. The pinnacle we had determined was the highpoint was in fact just a "ridge bump". So, back to collect our packs and pick another route to contour us across the formidable looking mountain side. Fortunately, Richard had already scouted this out while Ken and I were busy higher up. So, back in formation, we were once again headed towards the "new" highpoint. Clamoring about at first on narrow ledges, we headed towards and then up a band of vertically oriented bands of crumbly third class rock which brought us to a saddle between two competing highpoints. From our vantage point, it wasn't quite clear which was the higher. The Mexican topo map indicated a benchmark (of sorts) to our SW, yet the point to our NE looked nearly as high. Both were close, but the SW option looked to be only a third class climb. So, we dropped our packs and scouted the last few hundred feet SW which went easier than expected. Arriving there in only a few minutes from the saddle, we immediately knew this was the higher of the two points. Confirming this was a Mexican-style benchmark, a crude patch of cement with a nail in it and the letters "BN". We had hoped for a register with Sheldon's name in it, but found nothing despite our frenetic search for history. We concluded this was a second ascent and left a new register. This was a great adventure, not to mention some spectacular scenery. Since it was still well before noon, we had time to savor the summit and enjoy a long break. Although the descent would be slow and tedious, we knew the route and could see the trucks below. The success of finding a good approach road did much to insure our summiting of this remote and lonely range highpoint.

Returning to the trucks by 1:30 PM, we had time to drive out and complete the circumnavigation of the range. We drove north past the deep sand and found a comfortable camp spot in a secluded wash several miles from the pavement. It was still afternoon and on schedule, we popped a bottle of cold Champagne to toast our accomplishments.

The next morning, we drove a short distance east on Mex Highway 2 to do the highpoint of the Sierra Tinajas Altas which is really an extension of AZ's Sierra de la Lechuguilla. We then had a great Chinese dinner at Tin Wah in San Luis Rio Colorado, Sonora, Mex. They are located at Av. Obregon y Calle 25 Esq (it's actually on the north side of Mex Hwy 2 on the eastern end of the city and is on a corner location). After dinner, it was a slow crawl through the border and we passed through Yuma, AZ at sunset.

During the dirt road drive in, we noticed what appeared to be several landing strips, presumably for contraband activities. Accompanying these were semi-fresh-looking hum-vee tracks staggered around the main road in somewhat erratic patterns. Furthermore, these landing strips had been "destroyed" by someone digging lateral trenches about every 50 feet. This would surely cause any pilot a crash landing. Our conclusion was this was/is/could be an area of potential contraband activity. Although we saw none during our visit, I think it prudent to always be aware of these conditions when climbing/hiking/traveling near the U.S./Mexican border.

Maps : USGS 1:125,000 El Centro Mexican 1:50,000 El Sahuaro (I11D89) AAA Baja California AAA Mexico

For more information on Charles Sheldon's (1867-1928) and his explorations, I recommend his book :

The Wilderness of the Southwest ISBN 0-87480-417-5

Charles Sheldon's quest for desert bighorn sheep and adventures with the Havasupai and Seri Indians.

University of Utah Press Salt Lake City, Utah 84112

Richard Carey
In the town of San Luis Rio Colorado go east on Mexico Hwy. #2. After traveling about 41 miles look for a white sign on your right by a dirt road which is 0.3 miles east of the 128KM post. From this road it is another 0.3 miles further east to a store at La Joyita near the 127KM post. For those with a GPS navigator the turn is at UTM: 776140E, 3571210N in zone 11S. Reset your odometer and go south on this good dirt road past the Biosphere Reserve sign. At 0.8 miles go right at a junction and at 1.5 miles go left at another junction. Continue on the best looking dirt road heading generally SW toward the mountain range. At 6.8 miles reach an old corral and the start of sandy conditions where 4WD will most likely be needed. Continue through the dunes on a track lined with trash to a junction at 12.0 miles where you can go straight/S or right/WSW around the range. This junction is at: 766820E, 3556140N. Continuing straight, the road goes south around the range and then west to a shack at 17.6 miles. Curve northwest and at about 18.2 miles turn off right/NE and drive in toward the base of the mountain. >From here the highpoint is about 1/2 mile east.

Hike NE up a canyon to a prominent saddle on the ridge north of the summit. From the saddle backtrack some and go over a little ridge and drop into a steep chute that leads south all the way up to the ridge. At a point in the chute about 100 ft. from the crest go right through a notch where you will see the true highpoint SW across a chute that slopes steeply down to the right (north). Contour left and make your way up a steep face to the ridge and then follow the ridge to the top. The ascent is class 3 with an elevation gain of 1500 ft. and takes about 2 1/4 hours. 1/97 RLC

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