Organ Mountains

Organ Mountains

The Organ Mountains are a rugged mountain range in southern New Mexico in the southwestern United States. They lie east of the city of Las Cruces, in Doña Ana County.

The Organ Mountains are near the southern end of a long line of mountains on the east side of the Rio Grande's rift valley. The range is nearly contiguous with the San Andres Mountains to the north and the Franklin Mountains to the south, but is very different geologically. Whereas the San Andres and Franklin Mountains are both formed from west-dipping fault blocks of mostly sedimentary strata (with limestone most prominent), the Organ Mountains are made primarily of igneous rock (intrusive granite and extrusive rhyolite). Their name reflects their similarity in appearance (particularly the granite "needles" in the highest part of the range) with pipes that would be part of a pipe organ.

The San Andres Mountains are separated from the Organ Mountains by the San Augustin Pass, through which U.S. Route 70 passes on its way to White Sands Missile Range, White Sands National Monument and Alamogordo. The Franklin Mountains are separated from the Organ Mountains by a 10-mile wide gap, most of which is part of Fort Bliss.

Geology

The Organ Mountains are made up of three major sections. On the north end is a narrow ridge of vertically-jointed Tertiary granite (more specifically, quartz monzonite) called The Needles. This is the most picturesque section and includes the tallest point in the range, Organ Needle at an elevation of 8,990 feet (2,740 m). On the south side of The Needles is a much wider section of extrusive igneous rock, mostly a purplish-gray rhyolite. This section forms the bulk of the mountain range and reaches heights nearly as great as The Needles. This section is cut in half by Soledad Canyon, which extends west from the east side of the range, separated by a low ridge from Bar Canyon on the west side. The third portion of the Organ Mountains consists of the Bishop's Cap Hills on the southwest side of the range and Rattlesnake Ridge on the southeast side of the range. This third section is much smaller and lower in elevation than the other sections of the range, and consists of fault-block limestone similar to that of the San Andres and Franklin Mountains.

Botany

The Organ Mountains may be the most botanically diverse mountain range in New Mexico, with approximately 870 vascular plant species. Several of these, including the Organ Mountains evening-primrose (Oenothera organensis) and smooth figwort (Scrophularia laevis), are endemic to the mountain range and occur only in small, scattered populations. The Organ Mountains also have surprisingly high diversity in ferns, with 30 of the 56 species reported for New Mexico occurring within it. The high diversity and endemism of the range makes the Organ Mountains a very rewarding destination for the botanically-inclined, as well as a focus of botanical study. The flora differs greatly between the three sections of the mountain range, with the two igneous sections (The Needles and the central extrusive portion) sharing relatively few species with the southern limestone portions. The limestone section includes some of the northernmost populations of lechuguilla (Agave lecheguilla), often considered an indicator species of the Chihuahuan Desert, whereas the igneous sections of the range include all of the endemic taxa and have botanical affinity with Madrean flora typical of the southeastern Arizona sky islands.

Hiking

Hiking in The Needles is usually done from the Aguirre Springs National Recreation Area, where visitors can hike from 5,600 feet up to 6,880 feet on the 4.5-mile Pine Tree Trail loop. This trail covers a wide ecological range, from lower-elevation mountain mahogany scrub to ponderosa pine woodland on its upper parts. Hiking in the central extrusive igneous portion of the range is usually done from Dripping Springs or Bar Canyon. Dripping Springs offers several interconnected trails along lower-elevation washes and the lower parts of steep, rugged canyons. Bar Canyon has a single loop trail, in a wide, low-elevation canyon. The southern limestone section is difficult to access and rarely visited. Bishop's Cap can be reached through rugged dirt roads, whereas Rattlesnake Ridge is entirely within Fort Bliss and inaccessible to the general public.

Another location is the BLM's Soledad Canyon Day Use Area.

See also

References

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