By Dan Koning, Senior Field Geologist
Sandia Mountains
May 30, 2025
There is a place in the lower part of the Sandia Mountains, east of Albuquerque, where you can see a lot
of fascinating geologic features relating to granitic intrusions. This place is called Piedra Lisa Canyon,
located about midway between the eastern ends of Candelaria and Menaul Avenues (parking location:
35.11250° N and -106.48831°W). Note, there are two “Piedra Lisa” canyons in the Sandia
Mountains—this is the southern one; the northern canyon lies south-southwest of Placitas.
The granite in Piedra Lisa Canyon is called the Sandia Granite, which is 1.45 billion years old and actually
a monzogranite to granodiorite. This igneous body intruded a package of older metamorphic rocks
(gneiss and schist) that can be seen northwest of Forest Road 333, which is the paved road leading to
the La Luz trailhead from the north end of Tramway Boulevard. I am not an expert on granite intrusions
nor the Precambrian, so this postcard is more about showing photographs of some neat outcrops and
not so much an explanation of the larger story (i.e., more of a “show” and less of a “tell”). Details of the
larger story, composition, and age of the Sandia Granite are presented in two New Mexico Geological
Society papers in the 2016 Fall Field Conference Guidebook (Grambling et al. and Holland et al.) as well
as two papers by Kirby et al. (1995).
From the parking area, walk east up the canyon for a ~400 yards. You then come to a major dry fall
(Photo 1). Note the light-colored dikes and veins of aplite cross-cutting the darker granite. The dark
splotches in the granite are xenoliths from the older metamorphic rocks. The aplite is composed of
relatively small (>3 mm based on memory) quartz and feldspar crystals. The aplite dikes and veins stick
out of the rock because aplite is more resistant to erosion than the host granite – probably due to its
finer-grained texture and also because it has much less biotite. I have noticed in the Sandia Mountains
that portions of granite containing more biotite tend to be more erodible, in some places crumbling with
pressure exerted by one’s hand. This is probably because the biotite weathers relatively quickly (oxidizes
into iron oxides and then may turn into clays like vermiculite or smectite), and this allows bigger crystals
in the granite, like feldspar, to pop out easier.
You can get around the dry fall on trails to the north and south of it. Do not climb the dry-fall
itself…people have gotten seriously hurt doing so. The next photos were mostly taken above the dry fall.
Photo 2 shows a close-up of the schistose rock composing a xenolith (just to the right of my finger).
There is a small pod of light-orange megacrystic feldspar + quartz within it. As the Sandia magma up-
welled deep in the crust, the metamorphic rocks composing the roof of the magma chamber peeled off
and dropped into the magma pool. They evidently didn’t melt much, and when the magma crystalized
into granite it retained these chunks of older rock.
Photo 3 is a close-up of an aplite dike cross-cutting the granite. There are a few xenoliths (yellow arrows)
above it. The lack of biotite in the aplite give it a lighter color (in addition to making it more resistant to
erosion).
Not only does the aplite intrude the granite, it can also cross the xenoliths. In Photo 4, you can see such
a cross-cutting relation. Note how the top of the xenolith has been sheared to the right near the aplite
vein, probably due to top-to-right movement of the granite (either completely molten or perhaps in a
mush that was partly magma and partly solid crystals).
Locally, the xenoliths can be concentrated or entrained into elongated pods or lenses, presumably by
magma currents. Such a concentration of xenoliths can be seen in Photo 5.
In addition to fine-grained aplites, megacrystic pegmatites also occur (Photo 6). The cm-scale minerals
include potassium feldspar (microline) and quartz.
I think Piedra Lisa Canyon is a great place to see features related to the Sandia Granite. It’s a short walk,
there are loads of cool outcrops, and it’s fun to scramble around its big dry fall and then continue hiking
up-canyon. Come here if you want to imaginatively swim through an underground lake of 1.45 billion-
year old magma, but watch out for the xenoliths!