Geology of Golden By Ken Shaw This short trip through and around Golden will enable the participant to view various geological features of the Golden area and gain an understanding of some of the processes involved in the formation of Table Mountain and the Dakota sandstone Hogback and some of the geologic hazards that exist today. We will also pay a visit to the Colorado School of Mines and view some of the exhibits on their Geologic Trail. Finally we will stop at the Triceratops Trail to see some dino tracks and an old clay mining pit.
Starting point: Intersection of 93 and 58. Stop 1: 1 mile north on 93 turn left on Iowa Dr then left again on Canyon Point Circle .3 miles to pedestrian trail on left side. Stop 2: From stop 1 return to Iowa Dr and continue east .6 miles to Ford St. Turn right on Ford and proceed .1 mile before turning into church on left. Stop 3: From stop 2 take Ford street .9 miles to 12 th st and turn right. Proceed .4 miles to Maple St. and turn left. Proceed .2 miles to the Colorado School of Mines. Stop 4: From stop 3 take Maple St. .2 miles to Elm St and turn left. Where Elm St. ends into 19 th st. turn right. Almost immediately turn left on Jones Rd. You will soon see signs for the Triceratops Trail.
North and South Table Mountains are remnants of volcanic eruptions some 63 million years ago. The lava flowed down into what was then a valley. After cooling it became very hard and resistant to erosion. Over time the surrounding highlands eroded leaving Table Mountain as the valleys high point. North and South Table Mountains originally formed as one mountain but have subsequently been split in two by erosion of the easterly flowing Clear Creek. North Table Mountain South Table Mountain Stop 1 Photo by Ken Shaw
In this closer view of the West flank of North Table Mountain notice the erosion resistant cap of extrusive Tertiary volcanics. The volcanics are primarily composed of monzonites and latites. These igneous rocks on top are extrusive meaning they formed at the earths surface. In this case they formed when molten lava cooled and hardened. Stop 2 Photo by Ken Shaw
As we pull back a bit notice how close these homes sit to the mountain. According to a US Geological Survey these homes sit within an area with a high potential for rock fall hazard. The rockfall hazard area exists in both unincorporated Jefferson County and the incorporated city of Golden. Jefferson county has declared the rockfall hazard are a “no-build” zone. The city of Golden, however, has decided to allow building. Erosion resistant doesn’t mean erosion proof. Mechanical weathering mainly through frost wedging can occur when water seeps into the various joints in the rocks. When this water freezes it expands and can fracture these rocks sending them tumbling towards the homes below. Stop 2 Photo by Ken Shaw
This map shows zones of low (L), moderate (M), and high (H) rockfall-hazard potential along the west flanks of North Table Mountain. Notice the curved roads in Golden leading into the rockfall-hazard area. Image from: http://fieldguides.gsapubs.org/content/1/1.full.pdf+html
North and South Table Mountains sit atop the Denver formation. The Denver Formation consists of Loosely cemented, tuffaceous sandstone, silty claystone, and andesitic conglomerate from the Cretaceous period. These materials erode easily except where protected by the erosion resistant material of North and South Table Mountians. Dakota Sandstone hogback Dakota Sandstone hogback Photo by Ken Shaw
Here we see the Dakota sandstone hogback at the north end of the valley. This formation stops abruptly and then picks up again at the south end of the valley as indicated on previous slide. The reason for this is the Golden Fault. The Golden Fault is a large Laramie thrust fault which has caused nearly 8000 feet of the Paleozoic and Mesozoic sedimentary section to sink. Stop 4 Photo by Ken Shaw
The Colorado School of Mines has an outdoor geologic trail that features seven outcrops with various geologic and paleontological points of interest, including fossilized dinosaur tracks, logs and these samples of local basalt from table mountain, gneiss and granite from around Colorado. Stop 3 Photo by Ken Shaw Photo by Ken Shaw Photo by Ken Shaw
Stop 4 The clay mined from this pit was deposited in lakes and swamps 68 million years ago in the late Cretaceous is part of the Laramie Formation. Uplift of the Rocky Mountains 67-55 million years ago tilted the rock strata to near vertical making clay mining easy. Miners simply dug down into the clay between vertical beds of sandstone. Photo by Ken Shaw
Stop 4 Due to its proximity of the Golden Fault, the quarry walls along the Triceratops Trail are closely monitored for movement and weakness. This single plumb bob gauges movement between the upper and lower portions of the wall. Photo by Ken Shaw