Last weekend, we hiked San Lorenzo (or Saint Lawrence) Canyon. The canyon is located about an hour south of Albuquerque and less than five miles west of I-25. It is jointly managed by the U.S. Fish & Wildlife Service (USFWS) and the U.S. Bureau of Land Management (BLM) as a primitive recreation area. A large rock face divides the canyon into lower and upper sections. The lower section, which we explored, is only about a mile and a half long and can be driven or hiked. The canyon ends at the Sevilleta National Wildlife Refuge boundary, which is off limits without permission. If you’re willing to scramble, there are a myriad of side canyons to explore.
We left Albuquerque on a chilly, sunny, fall morning. Most directions to the canyon recommend a vehicle with high-ground clearance and/or 4-wheel drive. However, we found neither was required; the road was in very good condition. We parked at the mouth of the canyon, geared up, and set out to explore. Temperatures were in the mid-40s. Our exertions were enough to keep us pleasantly warm without the need for jackets. We had a light breeze to cool us. Since the canyon is so short and such an easy walk, we decided to explore some of the side canyons. Scrambling up and down, bushwhacking through the countryside, we had an enjoyable three-hour hike.
San Lorenzo Canyon is made up of sandstone cliffs, slickenside walls, and hoodoos that line both sides of a (normally) dry creek bed. The geology is complex with evidence of tectonic plate movement, erosion, and volcanic intrusion.
The mouth of the canyon is guarded by a textbook example of the Rio Grande Rift: a huge mesa-like formation called an angular unconformity. This small isolated mesa looks like a loaf of sliced bread topped by a horizontal cap. The tilted beds of sand- and mud-stone are about 7 to 10 million years old and the horizontal cap is about 0.5 million years old. The formation was created on an extremely large plain as layers of sediment were laid down on the plain and, over time, drainage channels cut into it. The layers were built horizontally then moving plates deep beneath the surface tilted the plain. Wind and water erosion have exposed the portion that is visible today.
This tilting is reflected on a larger scale throughout the canyon. As you look at the formations, you can see how the layers tilt in various directions because of the movement that occurs along several faults at work in the area. The large rock blocks have slipped and tilted, much like books on a shelf. Evidence of this motion can be seen in sheer walls with polished striations all in the same direction. These marks, called “slick-sides” or slickensides (yes, that is the proper geologic term), are formed when moving fault blocks grind across each other.
We have posted a gallery of photos from the tour: San Lorenzo Canyon. Enjoy!