Gift of the Magma
Created by the fiery interior of the earth some 32 million years ago, the Organ Mountains today are home to one of New Mexico's most diverse ecosystems.
by Jay W. Sharp
"The Organ Mountains, one of the most picturesque and rugged mountain ranges in the Southwest, form the skyline approximately 10 miles east of Las Cruces, New Mexico…, in southern Doña Ana County," wrote William R. Seager in his 1981 report, Geology of Organ Mountains and Southern San Andres Mountains.
Organ Mountains, west side, showing a stand of a
few of the range’s vascular plants. (Photos by Jay W. Sharp)
"The row of jutting, fluted, bare-rock pinnacles known as the Needles — the backbone of the range — can be seen on a favorable day from nearly 100 miles away, making them probably the most familiar landmark in the region…. Their stark, sawtooth profile, their challenging slopes and changing moods have made the Needles a favorite of artists, photographers and mountain climbers… as well as a daily pleasure to the people who live within their view."
According to some sources, the "jutting, fluted, bare-rock pinnacles" reminded early (and probably homesick) Spaniards of the pipes of the organs in the cathedrals of their faraway homeland, and that gave rise to the name for the range.
Basic Geologic History
The Organ Mountain range is one of 10 in New Mexico that parallel the eastern edge of the Rio Grande Rift — a 50-million-year-old fracture that has roiled the earth's crust and defined our historic river's course from Colorado southward through New Mexico's heartland.
Intermittent waterfall on the upper end of Fillmore Canyon.
The Organs' beginnings can be traced back some 32 million years, when magma from the earth's interior rose to intrude into depositional strata laid down by warm shallow seas hundreds of millions of years earlier.
In the northern parts of the range, the magma cooled and solidified before it erupted, and the sedimentary overburden eroded away over time, revealing those craggy, light-gray rock pinnacles, the Needles. The remnants of depositional strata remain today at the foot of the pinnacles. The Needles rise to about 9,000 feet elevation, nearly a mile above the surrounding Chihuahuan Desert floor.
In the southern part of the range, the magma did burst through the sedimentary strata, ejecting lava, rock and ash over 100 square miles of the landscape, according to the Bureau of Land Management. This raised mountains but also triggered a structural collapse that we now call the Organ Caldera.
By comparison, the San Andres Mountains and Franklin Mountains — other ranges paralleling the east side of the Rio Grande Rift, just north and south of the Organs — formed tens of millions of years ago not from volcanic flows but from the depositional strata laid down by the ancient seas. Driven by the tectonic forces of our planet, mountainous blocks of the stratified land fractured, rose, fell, tilted, buckled and folded — dipping generally to the west. Both the San Andres and the Franklins have relatively minor igneous (volcanic) rock exposures.
Over time, the Organs, with their volcanic origins, developed more varied topographical features, rainfall patterns and environmental niches from the desert floor up to the mountain peaks. The range became home for more diverse communities of desert organisms, which have been especially nurtured in the narrow canyons that receive water funneled down from the bare rock pinnacles.
Organisms Small and Big
Altogether, the Organ Mountain range — probably the most botanically diverse range in all of New Mexico — hosts, for example, some 870 vascular plant species (plants with tissues that conduct water, minerals and other materials through the roots, stems and leaves). These include not only several rare species — some growing nowhere else on earth — but also, surprisingly, some 30 species of fern, possibly more than any other mountain range in our state.
The Organs also serve as home for various species of nonvascular plants, or bryophytes — small herbaceous plants that form thick mats on rock and soil surfaces or tree trunks. These include some 87 species of the mosses and 8 species of liverworts, according to authorities Lloyd R. Stark and Richard C. Castetter. The bryophytes are the oldest types of plants on earth.
Greater earless lizard in a courtship stance, on the trail from the visitor center to Dripping Springs.
In many areas, the Organs' rocky slopes support wide swaths of lichen, a colorful interdependent union between a fungus and an algae. The fungus gives the lichen colony shape and form, soaks up water and nutrients, and provides reproductive features. The algae feeds the colony through photosynthesis, which yields the carbohydrates essential for survival. The lichen produces an acid that eventually breaks down its stony home to produce new soils.
Between the desert floor and the higher peaks, the Organs embrace three "life zones," variably nourished — says the Bureau of Land Management — by from 3 to 21 inches of rainfall annually, with the heaviest precipitation typically occurring at the higher elevations. Each zone is defined by the "plant and animal distributions as influenced by elevation, temperature, moisture and exposure." The zones grade one into the other with variations within each.
The lowest of the three — labeled the Lower Sonoran Life Zone by biological scientists — extends from the desert floor up the mountain slopes to about 5,000 feet. It hosts varied plant species with the dominant including mesquite, creosote and grama grasses. The second highest life zone — the Upper Sonoran — extends from about 5,000 feet upward to some 7,500 feet. Its dominant plant species include various oaks, junipers and acacias. The third and highest life zone in the Organs — the Transition Life Zone — ranges upward from some 7,500 feet to near the top. It features Ponderosa pine, oaks, junipers and mountain mahogany.
"In the rugged topography of the Organ Mountains a high degree of microenvironmental variation occurs in large stands," noted W.A. Dick-Peddie and W.H. Moir in Vegetation of the Organ Mountains, New Mexico. "…the activities of deer, and micropatterns of drainage, runoff and erosion in large randomly located stands all contribute to the diversity."
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