Goemmer Butte Vicinity

James S. Aber
Emporia State University

Goemmer Butte

Goemmer Butte is a relatively small, but conspicuous feature in the Cuchara valley near La Veta. It is named for the Goemmer (pronounced gimmer) Brothers ranch, which includes the butte. The butte consists of a steep-sided knob rising from a conical base. Cuchara Formation sandstone is well exposed around the margin of the butte. Goemmer Butte is composed of two kinds of rock (Lindsey 1995).

  1. Trachyte -- The central plug and dikes contain trachyte, which is high in potassium and sodium, but has slightly less silica than does rhyolite. Trachyte is the aphanitic equivalent of syenite--see igneous rocks.

  2. Breccia -- Breccia is a mixture of broken rock fragments set in a fine matrix. The breccia forms a crescent-shaped pipe that partly encloses the south, west and north sides of the trachyte plug. The breccia includes fragments of trachyte and Cuchara Formation sandstone.

Goemmer Butte is the low, brown knob to left with West Spanish Peak visible in the background. The butte peak, at 8043 feet, stands more than 1600 feet (500 m) above the surrounding terrace surface (foreground). Image date 3/99; © J.S. Aber.
View of the south side of Goemmer Butte. The main body of the butte is made up of intrusive rock, and the lower south side contains breccia (broken/crushed rock). Image date 6/99; © J.S. Aber.

Goemmer Butte is considered by some to be a "volcanic plug" in which magma vented to the surface (Penn and Lindsey 1996). The evidence for this volcanic interpretation is the breccia pipe that partly surrounds the butte's core. Breccia is associated with explosive volcanic eruptions in which pre-existing rocks are broken, mixed, and violently ejected by high-pressure gas/steam explosions. In this case, rocks derived from the surrounding Cuchara Formation and the trachyte plug make up the breccia. This implies that the breccia pipe must be younger than the trachyte plug. Goemmer Butte is considered to be Miocene, although its exact age and relationship to other intrusions of the region are uncertain (Lindsey 1995).

Breccia zone on the south side of Goemmer Butte. Note the unusual weathering pattern of vertical pillars. Image date 6/99; © J.S. Aber.
Closeup view of breccia from the south side of Goemmer Butte. Note the broken rock fragments within the boulder as well as covering by brightly colored lichens (orange, yellow, green). Image date 6/99; © J.S. Aber.

Culebra Range Foothills

Foothills of the Culebra Range rise abruptly, a few miles west of Goemmer Butte at Sulfur Springs. The margin of the foothills is marked by a conspicuous hogback formed in the Lower Cretaceous Purgatoire Formation and Dakota Sandstone. The Lytle Sandstone Member of the Purgatoire Formation supports the main hogback--see Monument Lake for further description of these lower Cretaceous strata. At Sulfur Springs, the strata are tilted up and overturned to the east against the main frontal thrust of the Culebra Range--see cross section below.

Sulfur Springs takes its name from springs that emit hydrogen-sulfide gas, where Indian Creek crosses the main frontal thrust. Many other springs are situated along the mountain front to the north and south.

Dakota hogback at Sulfur Springs, west of Goemmer Butte. The hogback is formed by resistant strata of the Purgatoire Formation and Dakota Sandstone. The strata have been tilted up and overturned (to the right) along the main frontal thrust of the Culebra Range, Sangre de Cristo Mountains. Image date 3/99; © J.S. Aber.

W-E cross section of the Culebra Range foothills in vicinity of Sulfur Springs, CO. Note overturning of strata at the mountain front. Green dot marks the hogback of the Purgatoire Formation and Dakota Sandstone (Kdp); red lines are dikes; east to right. Adapted from Lindsey (1995).

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GO 547/ES 747 © J.S. Aber (2002).