Fountain Formation
Encyclopedia
The Fountain Formation is a Pennsylvanian
bedrock unit consisting primarily of conglomerate
, sandstone
, or arkose
, in the states of Colorado
and Wyoming
in the USA, along the east side of the Front Range
of the Rocky Mountains
, and along the west edge of the Denver Basin
.
in El Paso County
.
overlies Precambrian
granite and gneiss. Outcrops of the formation typically dip steeply to the east.
s.
The characteristic predominant red color and the composition of the Fountain reflect that of the granite
s and gneiss
es from which it was eroded.
. Invertebrates include bryozoa
ns, brachiopod
s, crinoid
s, echinoids
, and gastropods
.
Plant fossils have been discovered in Garden Park north of Cañon City
, including Lepidophloios laricinus, Sigillaria, Syringodendron sp., Lepidophyloides sp., Lepidostrobus sp., Lepidostrobophyllum sp., Calamites, Neuropterus sp., Cyclopteris sp., and Stigmaria ficoides.
age, and are between 290 and 296 million years old.
Pennsylvanian
The Pennsylvanian is, in the ICS geologic timescale, the younger of two subperiods of the Carboniferous Period. It lasted from roughly . As with most other geochronologic units, the rock beds that define the Pennsylvanian are well identified, but the exact date of the start and end are uncertain...
bedrock unit consisting primarily of conglomerate
Conglomerate (geology)
A conglomerate is a rock consisting of individual clasts within a finer-grained matrix that have become cemented together. Conglomerates are sedimentary rocks consisting of rounded fragments and are thus differentiated from breccias, which consist of angular clasts...
, sandstone
Sandstone
Sandstone is a sedimentary rock composed mainly of sand-sized minerals or rock grains.Most sandstone is composed of quartz and/or feldspar because these are the most common minerals in the Earth's crust. Like sand, sandstone may be any colour, but the most common colours are tan, brown, yellow,...
, or arkose
Arkose
Arkose is a detrital sedimentary rock, specifically a type of sandstone containing at least 25% feldspar. Arkosic sand is sand that is similarly rich in feldspar, and thus the potential precursor of arkose....
, in the states of Colorado
Colorado
Colorado is a U.S. state that encompasses much of the Rocky Mountains as well as the northeastern portion of the Colorado Plateau and the western edge of the Great Plains...
and Wyoming
Wyoming
Wyoming is a state in the mountain region of the Western United States. The western two thirds of the state is covered mostly with the mountain ranges and rangelands in the foothills of the Eastern Rocky Mountains, while the eastern third of the state is high elevation prairie known as the High...
in the USA, along the east side of the Front Range
Front Range
The Front Range is a mountain range of the Southern Rocky Mountains of North America located in the north-central portion of the U.S. State of Colorado and southeastern portion of the U.S. State of Wyoming. It is the first mountain range encountered moving west along the 40th parallel north across...
of the Rocky Mountains
Rocky Mountains
The Rocky Mountains are a major mountain range in western North America. The Rocky Mountains stretch more than from the northernmost part of British Columbia, in western Canada, to New Mexico, in the southwestern United States...
, and along the west edge of the Denver Basin
Denver Basin
The Denver Basin, sometimes also called the Julesburg Basin, Denver-Julesburg Basin , or the D-J Basin, is a geologic structural basin centered in eastern Colorado in the United States, but extending into southeast Wyoming, western Nebraska, and western Kansas...
.
Origin of name
The Fountain Formation was named by geologist W. C. Cross in 1894 for exposures along Fountain CreekFountain Creek
Fountain Creek is a stream in El Paso and Pueblo counties, in Colorado in the United States.-Geography:From its source near the city of Woodland Park north of Pikes Peak, the creek flows southeast through the communities of Green Mountain Falls and Chipita Park to the town of Cascade. It...
in El Paso County
El Paso County, Colorado
El Paso County is the most populous of the 64 counties of the state of Colorado of the United States, now more populous than Denver County. The United States Census Bureau concluded that the county population was 622,371 in 2010. In recent years, the population had come closer to that of Denver...
.
Stratigraphy
The Fountain unconformablyUnconformity
An unconformity is a buried erosion surface separating two rock masses or strata of different ages, indicating that sediment deposition was not continuous. In general, the older layer was exposed to erosion for an interval of time before deposition of the younger, but the term is used to describe...
overlies Precambrian
Precambrian
The Precambrian is the name which describes the large span of time in Earth's history before the current Phanerozoic Eon, and is a Supereon divided into several eons of the geologic time scale...
granite and gneiss. Outcrops of the formation typically dip steeply to the east.
Depositional environment
The formation was formed by the erosion of the Ancestral Rocky Mountains, and deposition by fluvial processes as alluvial fanAlluvial fan
An alluvial fan is a fan-shaped deposit formed where a fast flowing stream flattens, slows, and spreads typically at the exit of a canyon onto a flatter plain. A convergence of neighboring alluvial fans into a single apron of deposits against a slope is called a bajada, or compound alluvial...
s.
The characteristic predominant red color and the composition of the Fountain reflect that of the granite
Granite
Granite is a common and widely occurring type of intrusive, felsic, igneous rock. Granite usually has a medium- to coarse-grained texture. Occasionally some individual crystals are larger than the groundmass, in which case the texture is known as porphyritic. A granitic rock with a porphyritic...
s and gneiss
Gneiss
Gneiss is a common and widely distributed type of rock formed by high-grade regional metamorphic processes from pre-existing formations that were originally either igneous or sedimentary rocks.-Etymology:...
es from which it was eroded.
Notable Exposures
- FlatironsFlatironsThe Flatirons are rock formations near Boulder, Colorado consisting of flatirons. There are five large, numbered Flatirons ranging from north to south along the east slope of Green Mountain, and the term "The Flatirons" sometimes refers to these five alone...
, near Boulder, ColoradoBoulder, ColoradoBoulder is the county seat and most populous city of Boulder County and the 11th most populous city in the U.S. state of Colorado. Boulder is located at the base of the foothills of the Rocky Mountains at an elevation of... - Garden of the GodsGarden of the GodsGarden of the Gods is a public park located in Colorado Springs, Colorado, USA.-Genesis of the park:Entrance to the park is free according to the wish of Charles Elliott Perkins, whose children donated the land to the city of Colorado Springs in 1909....
- Roxborough State ParkRoxborough State ParkRoxborough State Park is a Colorado State Park known for dramatic red sandstone formations. Located in Douglas County south of Denver, Colorado, the park was established in 1975. In 1980 it was recognized as a National Natural Landmark.-Geography:...
- Red Rocks ParkRed Rocks ParkRed Rocks Park is a mountain park in Jefferson County, Colorado, owned and maintained by the city of Denver as part of the Denver Mountain Parks system. The park is known for its very large red sandstone outcrops. Many of these rock formations within the park have names, from the mushroom-shaped...
and Amphitheater, Golden, ColoradoGolden, ColoradoThe City of Golden is a home rule municipality that is the county seat of Jefferson County, Colorado, United States. Golden lies along Clear Creek at the edge of the foothills of the Front Range of the Rocky Mountains. Founded during the Pike's Peak Gold Rush on 16 June 1859, the mining camp was...
.
Fossils
Marine invertebrates have been discovered in a limestone and shale member of the Fountain Formation, outcropping on a low hogback in Perry ParkPerry Park, Colorado
Perry Park is a census-designated place in Douglas County, Colorado, United States. The population was 1,180 at the 2000 census.-Geography:Perry Park is located at ....
. Invertebrates include bryozoa
Bryozoa
The Bryozoa, also known as Ectoprocta or commonly as moss animals, are a phylum of aquatic invertebrate animals. Typically about long, they are filter feeders that sieve food particles out of the water using a retractable lophophore, a "crown" of tentacles lined with cilia...
ns, brachiopod
Brachiopod
Brachiopods are a phylum of marine animals that have hard "valves" on the upper and lower surfaces, unlike the left and right arrangement in bivalve molluscs. Brachiopod valves are hinged at the rear end, while the front can be opened for feeding or closed for protection...
s, crinoid
Crinoid
Crinoids are marine animals that make up the class Crinoidea of the echinoderms . Crinoidea comes from the Greek word krinon, "a lily", and eidos, "form". They live both in shallow water and in depths as great as 6,000 meters. Sea lilies refer to the crinoids which, in their adult form, are...
s, echinoids
Sea urchin
Sea urchins or urchins are small, spiny, globular animals which, with their close kin, such as sand dollars, constitute the class Echinoidea of the echinoderm phylum. They inhabit all oceans. Their shell, or "test", is round and spiny, typically from across. Common colors include black and dull...
, and gastropods
Gastropoda
The Gastropoda or gastropods, more commonly known as snails and slugs, are a large taxonomic class within the phylum Mollusca. The class Gastropoda includes snails and slugs of all kinds and all sizes from microscopic to quite large...
.
Plant fossils have been discovered in Garden Park north of Cañon City
Cañon City, Colorado
The City of Cañon City is a Home Rule Municipality that is the county seat and the most populous city of Fremont County, State of Colorado. The United States Census Bureau estimated that the city population was 16,000 in 2005. Cañon City is noted for being the location of nine state and four ...
, including Lepidophloios laricinus, Sigillaria, Syringodendron sp., Lepidophyloides sp., Lepidostrobus sp., Lepidostrobophyllum sp., Calamites, Neuropterus sp., Cyclopteris sp., and Stigmaria ficoides.
Age
Rocks of the Fountain Formation are considered to be of Late PennsylvanianPennsylvanian
The Pennsylvanian is, in the ICS geologic timescale, the younger of two subperiods of the Carboniferous Period. It lasted from roughly . As with most other geochronologic units, the rock beds that define the Pennsylvanian are well identified, but the exact date of the start and end are uncertain...
age, and are between 290 and 296 million years old.