Glaciation of Culebra Range
and Cucharas Creek valley

James S. Aber
GO 547 & ES 747


During the Pleistocene Epoch, the Culebra Range supported many alpine glaciers. On the east side of Trinchera Peak, three glacial valleys descend toward Cucharas Creek valley (Ray 1940). Glaciers within these three valleys joined to form a single glacier that flowed down to a maximum lower limit about 10,000 feet elevation during the Pinedale glaciation (see Table I). Older glaciations are poorly represented in the vicinity.

Table I. Composite stratigraphy of Pleistocene glaciations in the southern Rocky Mountains, Colorado and northern New Mexico. Based on Richmond (1965, 1986) and Armour et al. (2002).
Glaciation Age Range* Oxygen-isotope
pre-Bull Lake 500,000-700,000
14 and 16
pre-Bull Lake 300,000 to 500,000
8 and 12
Bull Lake 130,000 to 300,000
6 (and 8)
Pinedale 12,000-23,000
Late Wisconsin

* Based on various radiometric and relative dating methods.

During retreat of the glacier, the ice limit stabilized around 10,400 feet elevation at a point where Cucharas Creek valley is constricted by resistant bedrock. A substantial recessional moraine accumulated at the junction of the three tributary glaciers at this position. Composed of lateral and end segments, the moraine complex dams several small lakes--Blue and Bear Lakes, which are the site of a National Forest campground today.

Aerial photograph of the Cuchara/Trinchera vicinity.

View of the Culebra Range from the east. Trinchera Peak (TP) is highest mountain to left. The heads of three glaciated valleys are marked by asterisks (*). Position of the major moraine in the Cucharas Creek valley is indicated. Image date 6/03; © J.S. Aber

The moraine at Blue and Bear Lakes is composed mainly of till, an unstratified and unsorted mixture of sand, gravel, silt, and clay sediment. Red and gray sandstone comprise the larger rock fragments, which are angular to subrounded in shape. Many bear striations, grooves, and other glacial markings. Numerous ridges, knobs, and kettle holes make for rough terrain within the moraine complex.

Upper Blue Lake with Trinchera Peak in the left background. Blue Lake is a "kettle lake" in the moraine complex within the valley of Cucharas Creek. This moraine was constructed during a recessional phase of the Pinedale glaciation. Image date 6/99; © J.S. Aber
Steven Veatch demonstrates till on the valley side above Blue Lake. The till consists of red and gray sandstone fragments within a finer matrix. He points to a thin bed of sandy sediment (darker color) within the till. Image date 6/99; © J.S. Aber

In the higher portions of the glacial valleys, till forms smaller recessional moraines. Erosional features include oversteepened bedrock steps, basins, cirques, and glacial pavements.

Trinchera Peak as seen from the arete ridge that extends north from the peak. Trinchera Peak is a classic alpine horn that was eroded and steeped by glaciers on its sides. Note the near-vertical position of rock strata of the peak. Image date 5/02; © J.S. Aber
View eastward from Trinchera Peak with West Spanish Peak in the distance. The valley in the foreground is the headwaters of Cucharas Creek. Bedrock steps, moraines, and cirques attest to the glacial origin of landforms in the valley. A - end moraine in upper valley, B - lateral moraine in upper valley, C - Blue-Bear Lake moraine in lower valley. Image date 8/01; © J.S. Aber
Tiny cirque on the northeastern side of Trinchera Peak. Note the bowl-shaped basin of the cirque and the lake at the center. This cirque was formed by a small glacier that occupied the basin. Image date 8/01; © J.S. Aber
View from Trinchera Peak toward the northwest. Sierra Blanca Peak is visible on the horizon. Trinchero Creek valley in the foreground descends quite steeply from Trinchera Peak (see next image). Image date 8/03; © J.S. Aber
Floor of Trinchero Creek valley on northwest side of Trinchera Peak. Note the glacial landforms with a small lake dammed behind a moraine. Image date 8/03; © J.S. Aber

Periglacial features
Trinchera vicinity

In the alpine zone (above treeline), strong frost action and deep ground freezing have produced periglacial features, such as patterned ground and rock glaciers (Wallace and Lindsey 1996). These features are postglacial and presumably date from cold episodes in the latest Pleistocene and Holocene (see Table II).

Table II. Composite stratigraphy of Holocene glaciations and periglacial episodes in the southern Rocky Mountains, Colorado and northern New Mexico. Based on Richmond (1986) and Armour et al. (2002).
Periglacial Episode
Age Range* Period
Grenadier, Temple Lake
Ptarmigan, Triple Lakes
9000 to 10,000 Younger Dryas
Earliest Holocene
Minimal glaciation or
periglacial phenomena
8000 to 5000 Altithermal
Early to mid-Holocene
Rock glaciers
2500 to 5000 Early Neoglacial
Late Holocene
Arapaho, Gannett Peak
Rock glaciers
120 to 400 Little Ice Age
Late Neoglacial

* Based on various radiometric and relative dating methods.

Overview of patterned ground on the crest of Trinchera Peak. Stones define a network of polygons. Orange survey flags mark a study grid. Image date 8/03; © J.S. Aber.
Jet Tilton demonstrates stone polygons on the crest of Trinchera Peak. Raised turf mounds are surrounded by shallow troughs filled with angular stones. Image date 8/01; © J.S. Aber.
Soil section in a turf mound of a typical stone polygon on Trinchera Peak. Well-developed A, B and C soil horizons indicate this feature has been stable for some time. Image date 8/03; © J.S. Aber.
Small rock glacier below a cliff of gray sandstone, Sangre de Cristo Formation, upper Cucharas Creek valley. The rock glacier has migrated in lobate form into a small cirque basin. Image date 8/01; © J.S. Aber.
Jet Tilton demonstrates the raised turf mound at the toe of a rock glacier in a small cirque basin, upper Cucharas Creek valley. Image date 8/01; © J.S. Aber.
Bighorn mountain sheep at the head of Cucharas Creek valley next to Trinchera Peak. Mountain sheep are common in the alpine zone of the Culebra Range. Vegetation here consists of low "cushion" plants that grow quite slowly. Image date 8/03; © J.S. Aber.

Patterned ground at Trinchera Peak (pdf file).

Subalpine bogs

Several kettleholes in the Blue-Bear lakes moraine contain bogs with substantial accumulation of peat during the Holocene. A peat core was collected from near the center of a typical bog to determine peat thickness and date the age of the basal peat. The core was 2 m long, and the basal peat yielded a conventional radiocarbon age of 342040 years before present (BP) with a corrected calendar date of 3700 to 3630 years BP (Beta 232587).

Peat core extracted from near the center of Beaver bog by field geology students. Left: coring tool extended to 2 m length. Right: core laid out on plastic. Below: closeup view of the basal end of the core. Photos taken June 2007.

This suggests that peat accumulation begin nearly four millennia ago during the early Neoglacial period of cooler, wetter climate in the late Holocene. Given a thickness of 2 m and maximum age of 3700 years, the average rate of peat accumulation is about two-thirds mm per year, which is typical for bogs in cold climates.

Return to Rocky Mts. geology homepage.
GO 547/ES 747 © J.S. Aber (2009).