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High Creek Fen: A Pocket of Unique Beauty & Diversity in the Southern Rocky Mountains

March 08, 2009  •  Leave a Comment

Descending Kenosha Pass and driving south toward Fairplay on U.S. Hwy. 285, South Park's expansive, high montane grassland fills the view out the windshield. This short, sparsely vegetated grassland is dominated by Festuca arizonica (Arizona fescue) and Muhlenbergia filiculmis (slimstem muhly) and covers much of South Park's 900 square mile (50x35 miles) valley floor. Walt Whitman noted from Kenosha Pass: "...South Park stretches fifty miles before me. Mountainous chains and peaks in every variety of perspective, every hue of vista, fringe the view, in nearer, or middle, or far-dim distance, or fade on the horizon."  The view out the windshield is immense and intimidating, yet welcoming. Sometimes it is necessary to overwhelm our spatial sense and temporal perspective in order to feel the intricacies of the Natural world—to feel apart of something as opposed to its oppressor. 

P8060013 South Park grassland in foreground. Spruce trees in background are growing in High Creek Fen.

South Park is one of four, large intermountain basins scattered north and south in Colorado’s Southern Rocky Mountains. South Park is about 80 miles southwest of Denver and the “Park” itself is delimited by the valley floor grassland contrasting with the forested slopes of the surrounding mountain ranges: the Mosquito Range to the west, the Park Range to the north, Tarryall Mountains and Puma Hills to the east, and the Black and Thirtynine Mile mountains to the south. Although much of South Park's valley floor is above 9,000 feet in elevation, this intermountain park only gets about 13 inches of rain each year due to the generally dry climate of the region exasperated by the imposing rainshadows of the surrounding mountains.

Location of South Park in Colorado.

High Creek fen is located at the blue maker. South Park is delimited
by the tan color to the north, south, and east of the marker.

After pulling out of Fairplay and driving south on Hwy. 285 a few miles, a strange cluster of spruce trees appears to the east of the highway.  The trees are completely out of place amidst the short-grass steppe of South Park's valley floor.  Taking a left turn off the highway and heading down a two-track, dirt road, High Creek Fen emerges from the high montane steppe revealing an immense area of wet ground.  Hummocks, pools, rivulets, and a creek; spruce trees, willows, bog birch, bulrushes, sedges, cottongrass, and aquatic plants all blanket the area.

P8060014  High Creek Fen in background

Although early botanical explorers had visited the site, it is a bit astonishing that the significance of High Creek Fen as a refugia for glacial relicts and haven for rare critters went unnoticed until 1990 when Dr. David Cooper recognized the unique character and biodiversity significance of this ecological Eden. What Dr. Cooper had stumbled upon is what many North American ecologists consider to be one of the rarest wetland types on the continent—a calcareous or extremely rich fen. Extremely rich fens differ from other fens due to the unique chemical quality of the groundwater that supports their existence—a preponderance of calcium, magnesium, and other nutrients which create a very basic (i.e. high pH) environment. There is some confusion in the scientific literature as to whether extremely rich and calcareous are synonymous terms. From what I can tell, calcareous is a subset of extremely rich, since other types of bedrock than limestone can result in high cation concentrations in groundwater (e.g. marine shale). Extremely rich fens are only found where groundwater is in contact with calcareous bedrock, such as limestone and dolomite, or other types of bedrock rich in cations. South Park is one of those places. Numerous extremely rich fens occur in the northern and western portion of South Park and High Creek Fen is one of the largest, most intact, floristically rich, and ecologically diverse extremely rich fens in Colorado.  It harbors more rare plants (14) than any other wetland in the state.  Because of its importance to global and regional biodiversity, the Nature Conservancy purchased the property and now manages it to preserve its unique biological character.

High Creek Fen's ecological diversity, uniqueness, and abundance of rare plants make it one of the most significant sites of biodiversity in the Southern Rocky Mountains.

The presence of such a large wetland in such a dry landscape is curious. High Creek is a meager stream and surely not large enough to wet such a large area. As a matter of fact, there is often no surface water in the channel before it enters High Creek Fen. It is not entirely clear why this is the case, but some researchers believe it may be (1) due to upstream diversions for agricultural use, or (2) due to the fact that as High Creek flows out of the mountains it 'loses' its flow to the underlying gravels and permeable limestone where it becomes groundwater, or (3) due to evaporation of the creek's meager flow prior to reaching High Creek Fen. Likely, all three factors may be at play. Regardless, High Creek Fen is wet…very wet.  What keeps such a large place, in such a dry climate, so soggy? Groundwater, and lots of it. The Nature Conservancy has conducted hydrogeologic studies of the site and believes that groundwater feeding High Creek Fen emerges from two major types of aquifers: a shallow aquifer associated with surficial glacial and alluvial (i.e. stream) deposits and a regional aquifer associated with the Leadville limestone formation. Discharge from these aquifers occurs throughout a variety of orifices—cobble beds, pools, springs, and floating mats. Groundwater discharge from gravel and cobble beds, outwash from past glaciation, can be seasonal or permanent. Cobble beds typically serve as the ‘headwaters’ of numerous rivulets which end up coalescenceing into larger channels and then proceed to sneak their way through the fen. These channels also pick up slow moving groundwater emerging from other sources such as springs, pools, and quagmires or floating mats.  All of this water eventually gets channeled back into our old friend, High Creek, which abruptly leaves the fen in the southeast corner with much more volume that when it entered the fen. 

Aerial view of High Creek Fen showing extent of wet ground and exit of High Creek in the southeast portion of the fen. Sodic flats (white areas) can also been seen near the mouth of the fen. (Google Maps)

High Creek in the central portion of High Creek Fen (the grayish shrub is Salix candida, a rare willow in Colorado restricted to calcareous fens.)

So where does all this groundwater come from? The shallow aquifer is likely supported by seasonal precipitation and streamflow in High Creek. The more stable and deeper aquifer is associated with limestone bedrock that was formed during the late Cambrian period when South Park was inundated by a series of advancing and retreating seas.  Sediments in this sea were deposited and over time converted to limestone and dolomite deposits found underneath South Park’s valley floor. These deposits were also uplifted and subsequently eroded by glaciers and streams when the Mosquito Range pushed upward. Thousands of years of snowmelt have found its way into these relatively porous bedrock formations forming a regional aquifer. Each year, as snowmelt rushes down the numerous creeks flowing out of the Mosquito Range, both the shallow and deep aquifer are recharged. Another important contributing factor to High Creek Fen’s unique quality is the interaction of its geological past and contemporary hydrology.  During the Pleistocene, mountain glaciers and their associated meltwaters tore apart the uplifted limestone and dolomite bedrock and deposited large quantities of sediment, gravel, and cobbles, derived from these calcareous formations, out into South Park’s valley floor.  Groundwater associated with the shallow aquifer comes into contact with this glacial outwash and, along with groundwater associated with the Leadville limestone aquifer (which emerges as springs throughout the site), is rich with dissolved calcium and magnesium.  These waters are the reason High Creek Fens supports such unique vegetation patterns, rare plants, mosses and invertebrates.

Possible groundwater flow of shallow and deep aquifers originating in the Mosquito Range and flowing southeast toward High Creek Fen (in red).

As you walk through the fen, the ecological effects of all this emerging groundwater are very apparent. The groundwater presents itself to the surface in a variety of ways. Already discussed above were the cobble beds, which support vegetation typical of gravel bars and small, spring-fed creeks.  Groundwater also emerges from springs in flat areas to form pools, water tracks, and sedge lawns. Some have referred to the shallow pools as quagmires due to their unstable, soft marly peat soils. Similar areas with a sturdier substrate are called floating mats. Floating mats are places where a thick mat of sedges sits on top of strong upwelling groundwater. Walking on these areas is like tromping across a waterbed. Serving as very shallow, linear aquatic corridors between individual quagmires and floating mats are water tracks. Quagmire, floating mats, and water tracks support similar types of vegetation dominated by Eleocharis quinqueflora (few-flowered spikerush), Triglochin spp. (arrowgrass), and Utricularia spp. (bladderwort). Eriophorum spp. (cottongrass) is often found growing along the edges of quagmires and on floating mats. Sedge lawns are dominated by Carex aquatilis (water sedge) and Carex simulata (analogue sedge).

 Quagmires and floating mats.

Sedge lawn spreading out from a spring.

Hummocky areas consists of both hummock and hollow topography. Small hummocks are covered by Kobresia simpliciuscula (simple bog sedge) and Trichophorum pumilum (little bulrush) while slightly taller and drier hummocks are capped with Kobresia myosuroides and Thalictrum alpinum (alpine meadowrue). Both vegetation types are considered to be globally rare with examples only known to occur in South Park, Convict Creek Basin in California (latter type), and Swamp Lake in Wyoming (former type). Hollows are the low troughs between hummocks.  Hollows support similar vegetation as found in water tracks.

Tall hummocks dominated by Kobresia myosuroides and Thalictrum alpinum.

Another unique area of the fen is toward the outlet. This area is not permanently inundated like the rest of the fen rather is wetted by capillary action of the soil. Evaporation on the soil surface results in the soil ‘pulling’ up moisture from a relatively shallow water table, leaving magnesium and sodium salts to accumulate on the soil surface. This area has much more sodium than the rest of the site and thus has been referred to as the sodic flats. Although you wouldn’t guess it by handling the soil, it is comprised of more than 20% organic matter which makes it an organic soil, or peat. Instead of calciphiles, halophytes such as Poa juncifolia (alkali bluegrass), Phlox sibirica (alpine phlox), and Glaux maritima (sea milkwort) are dominant on these sodic peats.


Sodic flats in the southeast corner of High Creek Fen.

As mentioned previously, High  Creek Fen supports an abundance of rare plants. Two species, Ptilagrostis porteri (Porter feathergrass) and Sisyrinchium pallidum (pale blue-eyed grass) are globally rare, both having the majority of their global range in the extremely rich fens of South Park. Ptilagrostis porteri occurs on the top of hummocks while Sisyrinchium pallidum occurs in alkaline wet meadows and occasionally in the fen itself. The remaining 12 plants are considered rare in Colorado but are more common when their global distribution is considered:  Carex livida (Livid sedge) is found in the sedge lawns; Carex scirpoidea (single-spike sedge) grows in wet meadows and on top of taller and slightly drier hummocks; Carex viridula (green sedge) is found in sedge lawns, water tracks, and at the base of hummocks; Eriophorum gracile (slender cottongrass) grow in sedge lawns and near quagmires; Lilium philadelphicum (wood lily) is found growing on the small ‘islands’ of spruce in the shaded understory; Packera pauciflora (few-flowered ragwort) is found in wet meadows; Primula egaliksensis (Greenland primrose) grows on hummocks; Salix candida (hoary willow) is found in sedge lawns and on low hummocks; Salix serissima (autumn willow) is found in sedge lawns and in areas with low hummocks; Trichophorum pumilum (little bulrush) grows on low hummocks; Utricularia ochroleuca (northern bladderwort) is found growing in the shallow waters of the quagmires and water tracks; and Salix myrtillifolia (blueberry willow) is found near springs or strong upwelling groundwater. Salix myrtillifolia was once thought to not occur south of where past continental glaciation occurred and its presence at High Creek Fen indicates the role this fen (and other extremely rich fens in South Park) has played as a refugia for glacial relicts.  Basically, as the climate warmed following Pleistocene glaciation, many arctic and boreal species disappeared from Colorado’s landscape or moved to higher elevations.  High Creek Fen provided a refuge for some of those species, and many still survive here today (e.g. many of the rare plants discussed above) despite their absence throughout the lower 48 states.

IMG_1973  Packera pauciflora, a rare species


Salix serissima (bright green shrub) and Salix candida (grayish shrub) with High Creek in foreground.


Salix myrtillifolia in center of photograph.

The rare Utricularia ochroleuca (on left) and common Utricularia macrorhiza (on right).

Salix candida.

Carex viridula.

In addition to the rare plants, researchers have also found rare insects at High Creek Fen. Nine aquatic beetles were collected here that are not known from anywhere else in Colorado, with four of those beetles occurring well south of their known range. An extremely rare caddisfly (Ochrotrichia susanae) was also found and is known from only one other location in the world. A rare moss, Scorpidium scorpoides is also found a High Creek Fen growing in the sluggish waters of quagmires, water tracks, and pools.

Spending the day at High Creek Fen is an easy way to get lost—in time and space. There are very few wetlands, let alone fens, in the Southern Rocky Mountains as large and as diverse as this site. Although I have never been to the true boreal or arctic reaches of the North American continent, when I’m immersed in High Creek Fen’s wilderness I definitely feel as if I’m in those far northern landscapes—and very far from anything I have ever experienced. Time slows to a pace where my thoughts are set free in the present and not burdened by thoughts of future or past events.  No matter how many times I have visited the site, that same feeling returns. Now that I live in Washington State, I am not sure when my next visit to High Creek Fen will be, but I very much look forward to that day. High Creek Fen’s beauty may be hidden in the vast steppe of South Park’s floor but it is not to be missed.

A wise, old, spruce tree keeping a close watch on its beloved home—High Creek Fen.


Sources: Sanderson, J. and M. March, 1996. Extreme Rich Fens of South Park, Colorado: Their Distribution, Identification, and Natural Heritage Significance.  Colorado Natural Heritage Program, Colorado State University.

Cooper, D.J. 1996. Water and soil chemistry, floristics, and phytosociology of the extreme rich High Creek fen, in South Park, Colorado, U.S.A. Can. J. Bot. 74:1801-1811.

Johnson, J.B. and D.A. Steingraeber. 2003. The vegetation and ecological gradients of calcareous mires in the South Park valley, Colorado. Can. J. Bot. 81: 201-219.


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