Classes offered by the Metropolitan State College of Denver. This website is not connected with the Metropolitan State College of Denver and the accuracy of the information on these pages is the sole responsibility of the author.

---=== Colorado Volcanic Landforms ===---

Purpose of the class

The CVL class takes the student on instructor-led explorations of various volcanic and volcanism related landforms in Colorado and northeastern New Mexico. The field trips provide "hands-on" experience in identifying various volcanic features and the associated rocks and minerals produced or promoted by volcanic processes.

This webpage describes the field trips taken on June 1 and 2, 2002.

North Table Mountain 6/1/02

The Table Mountains near Golden, CO were formed by the erosion of thick alluvial formations which were deposited by runoff from the newly uplifted Rocky Mountains just to the west. Parts of those deposits were capped by erosion resistant lava flows and as neighboring deposits were eroded away, the North and South Table Mountains were left standing above the resulting floor (1). We visited North Table Mountain to inspect its structure and identify several lava flows exposed along the flanks and top of the mountain. We also identified particular characteristics of the basalts and minerals contained in each separate lava flow. This field trip was led by Beth Simmons of the MSCD Geology Department.

	North Table Mountain from Golden. At far-left center, seen just above the houses, is the oldest flow; Lava Flow One. Following the slope up to the right, you will see Lava Flow Two and the top of the mountain is capped by Lava Flow Three. The Golden Fault trends north here and is indicated by the cottonwood trees in the foreground growing along a creek which follows the fault.
The west face of North Table Mountain from the "Loaf & Jug" parking lot off of highway 93 in Golden, CO. Looking NNE.

	The access to North Table Mountain is about a mile north of the "Loaf & Jug" on highway 93. The Golden Fault lies just to the right of the highway (green area). At left center is the exposed neck of the volcano suspected of producing the lava flows we are investigating in and on North Table Mountain.
From the old quarry road inside the North Table Mountain Open-Space Preserve, looking north.

An old road leads up the west side of the mountain to an abandoned rock quarry. Block basalt taken from the quarry was used to "pave" the old Denver tramway line and crushed basalt was used as road fill. Beth is pointing out characteristics of the flow as Larry tapes things for a documentary. All of the lava flows on North Table Mountain are composed of an igneous rock called basalt. This basalt may have come up from considerable depths through fractures and cracks in the Earth's crust. Note the cottonwood trees growing near a small spring which emerges here.

North Table Mountain Lava Flow One from the quarry road.

Just uphill from Flow One is an exposed layer of volcanic ash (the light colored layer), presumably erupted from the same volcano which produced the lava flows. Volcanic ash can be transported long distances in the atmosphere and be deposited far from the site of its eruption. Ash deposits may lithify over time, or thick, hot deposits of ash may "weld" together. Both processes form a rock-like substance called "tuff". Tuff can be worked with tools made of harder rocks and many ancient cliff dwellings in the Southwest, such as at Bandelier, were carved into tuff layers.

Exposed sediment layers along North Table Mountain quarry road.

One of the sedimentary layers just below Lava Flow Two contains the lithified remains of a common volcanic event; a lahar. Lahars are mudflows which develop when the loosely consolidated ash and tephra from an eruption is remobilized by water, either from precipitation or from meltwater generated by volcanic activity. Lahars are extremely destructive and have caused thousands of deaths near volcanoes in recorded history. The mud is a dense liquid and can transport boulders weighing thousands of pounds within its flow. This image shows a weathered conglomerate containing pebble and cobble sized gravel.

Evidence of an ancient mudflow; lithified lahar remains along North Table Mountain quarry road.

	Further up, we come to Flow Two and take a quick break. Don't be fooled; it was very hot and humid that day. Beth is talking about thick sedimentary deposits which covered Flow Two and the resulting effects the deposits had on the igneous rock below.
Base of Lava Flow Two, North Table Mountain.

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Notes
(1) The Table Mountains are more accurately described as "mesas" than as "mountains", but I will use their traditional names.  Back