Monday, May 14, 2018

The Mailbox on the Sill—the short & the long of it

The Palisades in Cimarron Canyon, northern New Mexico.
Browsing through my photos of the Cimarron Canyon Palisades, I spotted an odd form on the crest which I hadn’t noticed when I was there. Is that really rock? Zooming in showed nothing to suggest otherwise. But how improbable!
I’m hardly the first to spot this weird finger of rock. Years ago someone thought it odd enough to add to the Devil’s collection of landforms and landmarks—Devil’s Postpile, Devil’s Backbone, Devil’s Thumb, Devil’s Racetrack, Devil’s Marbles, Devil’s Gate, etc. In this case, we have the Devil’s Mailbox.
Devil’s Mailbox; Pomona Public Library, Frasher Foto Postcard Collection, 1938.
Unfortunately, the Mailbox story ends here, as my “research” (Google) produced no further details. In contrast, the story of its context is much longer, on the order of 40 million years. The Mailbox is part of the Palisades sill, a massive sheet of igneous rock intruded into sedimentary strata of the Cimarron Range. This may have happened during creation of the range, part of the Laramide Orogeny, the mountain-building episode that built the Rocky Mountains. In a later episode of uplift, maybe 20 or 30  million years ago, the Cimarron River cut down through the range revealing part of the sill, in cross-section. The dramatic exposure is called the Palisades, and is part of Cimarron State Park. There’s a convenient pullout at the base, along US Highway 64.
Actually, the details are still being debated.
As of 2002, geologists were still debating the exact age and composition of the sill. Dating has produced ages ranging from 35 million years to as young as 26 million. Rock composition also has been hard to pin down (see this page for citations):
“Based on mineralogy and chemical composition, the Palisades consist of biotite-diorite porphyry. Other geologists have called the rock type of the Palisades a monzonite porphyry, quartz monzonite porphyry, dacite porphyry, a granodiorite porphyry, or a transition from trachydacite to dacite. Although these terms describe the rock properly according to its composition, some terms are inconsistent with its texture. Therefore, the term porphyritic dacite seems the best description of these sills.”
The rock looked porphyritic to me, i.e., large phenocrysts in a matrix of fine-grained rock. This is easy to see in the blocks lining the pullout.
The columns and towers of the exposed sill are spectacular. They're separated by long vertical joints that formed as the intruded magma cooled, underground. Later, water seeped into the fractures, and froze and expanded in winter, slowly breaking the rock. This went on for millennia, producing talus slopes at the base (and rock blocks for the pullout).
Talus slope at base, apparently stable enough for trees to grow large. 
The Palisades Sill Official Scenic Historic Marker is on US Highway 64 in Cimarron Canyon State Park, about 8.3 miles east of Eagle Nest and 15.5 miles west of the town of Cimarron (36.537449° -105.152374°). The Mailbox stands near the northwest end of the ridge visible from the highway.

Sources

The Palisades sill is included in New Mexico’s Virtual Geologic Tour, a terrific trip-planning resource. The Cimarron Canyon State Park page includes a substantial list of references.


Monday, May 7, 2018

Boxelder News: some sensationalism this month

Photo by M Nelson.
The standard approach shot—boxelder in shady nook, with no obvious changes.
When I rounded the corner of the warehouse yesterday, on my monthly tree-following visit, I could see no obvious changes in the boxelder. But as I got closer, I saw that its neighbors were coming to life, like dandelions along the ramp to the warehouse door.
And what looked like windblown debris from a distance turned out to be sand dock, Rumex venosus, currently in bud. The red winged fruits are spectacular, but we will have to wait at least a month for those.
Sand dock in bud.
As for the boxelder … buds were opening, but only on one branchlet, one of the first to catch sun in the afternoon. These look like flowers buds with emerging anthers, therefore a male tree.
Male boxelder flowers, photo by Kruczy89; source.

Meanwhile, 177 miles south of Laramie and about a thousand feet lower, a boxelder at Lowe’s is fully leafed out, displaying fresh green foliage with a hint of copper. In summer, the leaves will be rich green, and then turn pale red in autumn—hence the name, Sensation Box Elder. It’s said to be “the best known plant discovery of Warren Carnefix, the Idaho plantsman and nurseryman whose family will mark 100 years in the nursery industry this year.” (J. Frank Schmidt & Son Co.)
Sensation Boxelder front center, among arboreal offerings at Lowe’s (M Nelson).
A hint of copper in spring leaves (M Nelson).
Fall foliage (source).
The Colorado Springs Rock Guy was surprised to find a boxelder in a nursery, having lived around boxelders and the notorious boxelder bugs as a kid in Kansas. “I have never, never seen anyone, at least from Kansas, plant a boxelder tree. I have seen many persons cut them down or grub them out.”

But according to J. Frank Schmidt, the “seedless nature of this male clone makes it less attractive to box elder bugs, a pesky but harmless insect [trees show no obvious signs of injury] that feeds on the flowers of female trees and takes refuge in houses in the fall.”

The University of Minnesota Extension says the same: “Starting in mid‑July, they [boxelder bugs] move to female seed-bearing boxelder trees where they lay eggs on trunks, branches, and leaves. They are rarely found on male boxelder trees.” Even female trees get the Extension’s support: “In our opinion, the benefits of having these trees in a landscape outweigh the problem of occasional infestations.”

More than a few people agree. There are even boxelder bug fans, some of whom adopt and name the invaders of their homes. See Thank Goodness for Boxelder Bugs by the Prairie Ecologist, and the numerous comments, almost all positive.


This is my May contribution to the virtual gathering of tree-followers, kindly hosted by The Squirrel Basket. More news here.