What the heck are fens? Unlike bogs, which are acidic, low in nutrients and dominated by sphagnum moss, fens are fed by mineral-rich groundwater, creating neutral or alkaline peatlands with a rich diversity of brown mosses, sedges, wildflowers and even carnivorous plants. Along the east slopes of the Cascades in Central Oregon, fens are rare, occurring only between 4,500’-6,000’ in isolated perched aquifers over slow-draining glacial till from the last Ice Age. Two secluded but accessible fens can be found near Little Cultus Lake.

Hydrology of the Little Cultus Fens

The most distinguishing feature of Central Oregon fens is that they are kept permanently wet by groundwater seepage, which maintains their soil saturation even through the dry summer months. This constant water supply, combined with the low permeability of the underlying glacial till and pumice deposits, creates a “perched” aquifer and water table — which are isolated and separate from the larger regional groundwater flow (see diagram).

The perennial water source for the Little Cultus fens is Benz Spring, which seeps directly into a small, quarter-acre Upper Fen at 4,900’. This water flow then continues underground for about a half-mile, dropping 60’ to a much larger, one-acre Lower Fen at 4,840’. Eventually, this groundwater seeps further downhill and feeds into Little Cultus Lake (see map download).

Age of the Little Cultus Fens

A second remarkable aspect of fens is the build up of peat deposits, due to the slow decomposition of plants in their waterlogged soils. Low dissolved oxygen and low water temperatures, plus the lack of fluctuation in water tables all contribute to the slow decomposition of plant residues. When the production of biomass is greater than its rate of chemical breakdown, peat accumulates in the soil.

A core sample taken from the Little Cultus Lower Fen showed peat deposits extending down 66” into the soil, or 5.5 feet. Studies of similar fens across Oregon and Washington indicate that peat accumulates at a rate of about one inch per century. Thus a rough estimate of the age of the Little Cultus fens is about 6,600 years.

Indicator Plants of Fen Wetlands

The third and final identifying feature of fens is the presence of certain indicator plants, which have specially adapted to the soggy environment. These include several species of brown moss, a few sedges and rushes, plus wildflowers such as bog orchid, primrose monkey flower, elephant’s head and bog saxifrage. Carnivorous plants, such as great sundew and oval sundew, can also be found — although we didn’t observe these in the Little Cultus fens.

Besides these special indicator plants, fens on the east slopes of the Central Oregon Cascades also host a variety of rare and sensitive plants. In fact, it’s estimated that of all the rare and uncommon plant species on Deschutes National Forest, 15%-20% are found in fen ecosystems. So please be respectful and extremely careful if visiting these delicate fen wetlands!

Visiting the Little Cultus Fens

The Lower and Upper fens are both located a short walking distance off Forest Road 4636, about a mile west of the Little Cultus Lake Campground (see map download below). The road is dirt, mostly single lane with turnouts, and has a few protruding rocks — but it can be negotiated with care by most passenger cars. Because of the thick trees, it’s easy to get disoriented in this area, so a few GPS reference points are also provided in a download below.

The best parking spot is a prominent turnout on Road 4363 (GPS Point 1), about 1.1 driving miles west of the campground. From the turnout, it’s a 75-yard walk north downhill through the trees and over a few deadfalls to the edge of the Lower Fen (GPS Point 2). There are a couple of old fallen, decomposed logs that extend out into the fen, from which one can inspect the fen plants up close, without stepping on them. Please do not walk out onto the wet and fragile moss beds!

Returning to the parking turnout, it’s a 0.6 mile walk (or drive) west up Road 4636 to reach a second trail to the Upper Fen. At a large round boulder just west off the road (GPS Point 3), look for a faint trail descending into the dry meadow to the west. Follow game trails west across this meadow for about 250 yards, through blueberry bushes and grassy patches, to its western edge. The game trail then continues for another 75 yards west through a thick stand of Engelmann spruce to the edge of the Upper Fen (GPS Point 4). Here, one needs to stay on dry land in the blueberry bushes around its edges, to avoid trampling the wet moss beds.

Download (PDF, 792 KB): Photos of Little Cultus Fens
Download (PDF, 665 KB): Map for Little Cultus Fens
Download (GPX, 1 KB): GPS Points for Little Cultus Fens

DISCLAIMER: Every effort has been made to ensure the accuracy of this information, but the authors do not guarantee that it is either current or correct. The reader assumes full responsibility for any use of this information, and is encouraged to exercise all due caution while recreating.