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Geology - Boulder - Denver - Golden and Lyons
The Front Range of Colorado marks the juxtaposition of the Great Plains and Rocky Mountains. This geologically complex transition zone runs north – south throughout Colorado and physically separates the state. Cities like Ft. Collins, Boulder, Golden and Colorado Springs lie at the eastern base where elevations rage from 5,000’ – 8,500’. The Front Range's granitic mountains came to be over billions of tumultuous years, a story compelling as the formations themselves:
Geologic History:
The oldest rocks in the Front Range are carbon dated at 1.7 billion years old, or simply “Precambrian”. The term Precambrian does not refer to an “era”, but rather a period 570 million years ago considered the first geologic time period of Earth. This Precambrian rock consists of both metamorphic and granitic rock; metamorphic rock being older and generally found in the foothills west of Boulder.
Buried deep below the newer strata, the Precambrian metamorphic rock experienced intense heat, pressure and succumbed to chemical reactions which created their present form. Schist, gneiss, and quartzite are the three most common types of metamorphic rock in Boulder’s Front Range.
Once an ocean…
Around 600 million years ago at the beginning of the Paleozoic era, the Front Range was gradually flooded by a vast ocean. In addition to other marine deposits, sand and lime mud was deposited on beaches and buried under other sedimentary rock, turning into the area’s sandstone and limestone. For the next 300 million years, the area would flood and recede, leaving layering deposits of sediment.
At around 300 million years ago, the Ancestral Rockies were formed. Tectonic activity pushed up 2 great mountain ranges in central and western Colorado bringing the deeply buried Precambrian metamorphic rock high above the surface of the Earth; and exposing it to erosion. As the Precambrian rock eroded, its sediment was carried away in all directions, settled and eventually formed the sandstone and shale rock called the Fountain Formation. While most have not heard of the Fountain Formation, those in Boulder’s Front Range see it every day. The Flatirons and Sanitas Ridge are both part of the Fountain Formation.
Lyons Sandstone
Around 260 million years ago (the Permian period), waters receded and great sand dunes inhabited the area, shifting and essentially burying the original Fountain Formation for the time being. The dunes, however, led to the creation of the Lyons Sandstone. Well known for its pinkish hue, the Lyons Sandstone is commonly used in building construction and cannot be missed when driving through the Front Range city of Lyons, Colorado. Hall Ranch Open Space in Lyons, a popular hiking and biking destination, provides a showcase of this sandstone for its visitors.
At the end of the Permian period, the Front Range was marked by vast floodplains. Ox bowing rivers carried silt and sediment from the mountains down to the east, covering the Lyons sandstone created in the Permian period.
At the start of the Cretaceous period around 140 million years ago, the sea invaded Colorado once again, this time from the north and south, leaving behind countless tons of varied sand and sediment. The next 100 million years are marked by continuous advances and retreat of the ocean. Shale, coal, limestone and sandstone were the most common layers of sedimentary rock associated with this period. Ultimately, at the end of the Cretaceous period, the ocean finally withdrew from Colorado.
There’s Gold in them thar’ hills
Around 70 million years ago, upon withdrawal of the ocean from Colorado in the late Cretaceous period, geologic forces began an era of zealous mountain building. Magma bubbled up through the existing mountains and foothills to create bigger mountains and foothills. The magma’s byproduct of sizzling hot mineralized water seeped through cracks in the existing rock leaving behind vast deposits of metallic ore. This was the beginning of Colorado’s geologic gold rush.
As magma spewed to the Earth’s surface from volcanoes, tectonic activity continued to shape the core of today’s Front Range and Rocky Mountains. It was during this time that Boulder’s famous Flatirons were formed. Shifting ground and tectonic uplift tilted the Fountain Formation on its side. As the Fountain Formation broke through the Earth’s surface, erosion set in and eventually formed Boulder’s Flatirons.
During these periods of mountain building and uplift, the deposits of crushed rock and debris were brought down to the eastern plains by water. The hills and mesas seen across the Front Range were created by these massive sedimentary deposits.
Today, the Front Range is experiencing a period of relative geologic calm. Volcanic activity is seen as dormant, tectonic activity is virtually non-existent and in general, the geologic picture is seen as stable.
Geologic History:
The oldest rocks in the Front Range are carbon dated at 1.7 billion years old, or simply “Precambrian”. The term Precambrian does not refer to an “era”, but rather a period 570 million years ago considered the first geologic time period of Earth. This Precambrian rock consists of both metamorphic and granitic rock; metamorphic rock being older and generally found in the foothills west of Boulder.
Buried deep below the newer strata, the Precambrian metamorphic rock experienced intense heat, pressure and succumbed to chemical reactions which created their present form. Schist, gneiss, and quartzite are the three most common types of metamorphic rock in Boulder’s Front Range.
Once an ocean…
Around 600 million years ago at the beginning of the Paleozoic era, the Front Range was gradually flooded by a vast ocean. In addition to other marine deposits, sand and lime mud was deposited on beaches and buried under other sedimentary rock, turning into the area’s sandstone and limestone. For the next 300 million years, the area would flood and recede, leaving layering deposits of sediment.
At around 300 million years ago, the Ancestral Rockies were formed. Tectonic activity pushed up 2 great mountain ranges in central and western Colorado bringing the deeply buried Precambrian metamorphic rock high above the surface of the Earth; and exposing it to erosion. As the Precambrian rock eroded, its sediment was carried away in all directions, settled and eventually formed the sandstone and shale rock called the Fountain Formation. While most have not heard of the Fountain Formation, those in Boulder’s Front Range see it every day. The Flatirons and Sanitas Ridge are both part of the Fountain Formation.
Lyons Sandstone
Around 260 million years ago (the Permian period), waters receded and great sand dunes inhabited the area, shifting and essentially burying the original Fountain Formation for the time being. The dunes, however, led to the creation of the Lyons Sandstone. Well known for its pinkish hue, the Lyons Sandstone is commonly used in building construction and cannot be missed when driving through the Front Range city of Lyons, Colorado. Hall Ranch Open Space in Lyons, a popular hiking and biking destination, provides a showcase of this sandstone for its visitors.
At the end of the Permian period, the Front Range was marked by vast floodplains. Ox bowing rivers carried silt and sediment from the mountains down to the east, covering the Lyons sandstone created in the Permian period.
At the start of the Cretaceous period around 140 million years ago, the sea invaded Colorado once again, this time from the north and south, leaving behind countless tons of varied sand and sediment. The next 100 million years are marked by continuous advances and retreat of the ocean. Shale, coal, limestone and sandstone were the most common layers of sedimentary rock associated with this period. Ultimately, at the end of the Cretaceous period, the ocean finally withdrew from Colorado.
There’s Gold in them thar’ hills
Around 70 million years ago, upon withdrawal of the ocean from Colorado in the late Cretaceous period, geologic forces began an era of zealous mountain building. Magma bubbled up through the existing mountains and foothills to create bigger mountains and foothills. The magma’s byproduct of sizzling hot mineralized water seeped through cracks in the existing rock leaving behind vast deposits of metallic ore. This was the beginning of Colorado’s geologic gold rush.
As magma spewed to the Earth’s surface from volcanoes, tectonic activity continued to shape the core of today’s Front Range and Rocky Mountains. It was during this time that Boulder’s famous Flatirons were formed. Shifting ground and tectonic uplift tilted the Fountain Formation on its side. As the Fountain Formation broke through the Earth’s surface, erosion set in and eventually formed Boulder’s Flatirons.
During these periods of mountain building and uplift, the deposits of crushed rock and debris were brought down to the eastern plains by water. The hills and mesas seen across the Front Range were created by these massive sedimentary deposits.
Today, the Front Range is experiencing a period of relative geologic calm. Volcanic activity is seen as dormant, tectonic activity is virtually non-existent and in general, the geologic picture is seen as stable.
