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Lava Flow Two was covered by thick sedimentary deposits. Water percolating down through those deposits picked up dissolved minerals which recrystallized within voids in the lava below. The light colored zeolites within the dark basalt are the result. |
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Basaltic lava from Flow Two, North Table Mountain.
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Dave takes a precarious position
from which to view the scenery. He is sitting on Lava Flow
Three basalt and looking west towards the Rockies. The
striped formation towards the top right of the image is a
length of the Dakota Hogback; sedimentary formations turned
upwards as the Rocky Mountains were uplifted during the
Laramide Orogeny (mountain building period).
The column of basalt that Dave is sitting on may some day wind up in the yard, or front room, of a house in the developments immediately below. Highway 93 runs left-to-right across the center of the image. |
| From the top of North Table Mountain, looking NW over houses in Golden, CO. |
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The last remnant of Flow Four which capped the
top of North Table Mountain. This flow is on the northwest
edge of the mountain and is not visible from below.
The composition of the magma which produced Flow Four changed somewhat as compared to the older flows and the basalt is weathering in a slab-like manner instead of the rectangular columnar fashion of the other three flows. |
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Lava Flow Four, North Table Mountain.
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"Honest, professor, my dog drowned my homework."
Shamus the Wonder Dog came along on the trip with us, complete with his own backpack. He found this muddy pond on top of the mountain and made a bee-line for it. Unfortunately, Shamus had Dave's homework in his backpack. Shamus would also dig up rocks and play with them whenever we stopped. Yep; he is an actual rock hound. |
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Shamus' revenge, North Table Mountain.
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After Table Mtn., we went north to Boulder to
see an unusual site; the Valmont Dike.
The dike is an exposed vertical, wall-like intrusion of magma. Normally, dikes occur in radial patterns around a central volcanic vent or other volcanic feature, but this is the only known exposure of this dike, or any other, in the Boulder vicinity. Nor is there any indication of a related vent in the area. This is the north face of the dike which lies completely within a private rock quarry. |
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Valmont Dike, Valmont, CO.
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Looking NE from inside the quarry.
The dike has sliced up vertically through the local sediments (note the horizontal gray layers in the center of the image) and erosion has exposed the top of the intrusion. The lighter colored sediment below the basalt top is the "baked zone" where the high temperature of the magma affected the original sediments, as seen on the lower slopes. Why this dike appears where it does is a mystery, but may indicate an as yet undiscovered volcanic vent lies nearby. The Valmont Dike was the last stop on Saturday. Tomorrow we head for Middle Park. |
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Valmont Dike as viewed from the southwest.
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