Once a shallow 2,000-acre lake, which was filled by volcanic ash during the eruption of Mt. Mazama 7,700 years ago, Big Marsh today is one of the largest, high-elevation wetland/marshes in the nation. A half-hour drive west of Highway 97 from Crescent, it’s a one-of-a-kind resource supporting a wide diversity of Central Oregon wildlife — from elk, to river otters, to sandhill cranes — plus the largest population of threatened spotted frogs in Oregon. A 2.4-mile cross-country ramble invites visitors to explore this natural wonder.

Hydrology of Big Marsh

As in much of Central Oregon, the annual flow of water from its glacier-carved, 30,000-acre watershed is crucial to Big Marsh. Before 1906, when the marsh fell from the public domain into private hands, early visitors reported that large beaver dams created water levels 12”-20” deep across the marsh. In the 1940s, deep drainage ditches were cut around the marsh to lower the water table and convert wetland to grassland in order to improve cattle grazing. Finally in 1982, the Forest Service acquired the marsh, ended cattle grazing, and has worked ever since to restore the natural functioning of the marsh hydrology by filling drainage ditches, removing encroaching lodgepole pines, and re-planting native marsh vegetation.

The water levels at Big Marsh fluctuate naturally with the seasons and the depth of winter snows in its watershed. Though rain-on-snow events during winter can increase runoff into the marsh, the vast majority comes during the spring snowmelt from April to June (see chart), sometimes flooding the marsh from tree line to tree line. The marsh then gradually dries out as the summer progresses, with water levels dropping to 6”-12” on the lower northern end and to 0”-4” on the higher southern end.

Oregon Spotted Frogs at Big Marsh

Why is Big Marsh such a unique haven for the federally-listed, threatened spotted frogs? For one, the Oregon spotted frog is the most aquatic of all native frog species in the Pacific Northwest. It has no terrestrial phase, and thus requires wetland habitat for all stages of its life cycle. It needs warm shallow water for egg and tadpole survival in the spring, deep partially-vegetated pools for juvenile and adult survival in the dry season, and perennial unfrozen water to protect all age classes during the cold winter months.

Also, studies indicate that the larger the marsh, the larger the successful breeding population of spotted frogs. Simply put, larger sites are more likely to provide all of the seasonal wetland microhabitats required by the frogs over their life cycle. Tadpoles need wetted channels to move out of the shallow, egg-laying sites to deeper pools for juvenile development — and all age classes need wetted channels to move into unfrozen overwintering water. Any gap in this chain of specific wetland types spells doom for Oregon spotted frog survival.

Field surveys in recent decades indicate just how successful the Forest Service’s marsh restoration efforts have been. In the mid-1990s, before restoration began, the number of breeding adult spotted frogs (male and female) was in the hundreds. Two decades later, the survey numbers are in the thousands, exceeding 7,000 breeding adults in 2015. Though annual population numbers fluctuate, the long-term population trend at Big Marsh is decidedly positive.

The Hike at Big Marsh

Years ago, there was a well-built, 2.6-mile loop trail at the eastern edge of Big Marsh, extending out along an old drainage canal and returning through the fir forest. However, this trail fell into disrepair and can barely be found today. The good news is that the Forest Service’s ongoing restoration efforts at Big Marsh include plans to re-establish and rebuild this old loop trail — but it has yet to be accomplished. As of mid-summer 2019, the east-side access road has been completely rebuilt, a new gravel parking area has been installed, and the old drainage canal is being reshaped into a series of ponds more accommodating to the Oregon spotted frogs.

Hikers today can still follow the old route out along the drainage canal, but it's currently a 1.2-mile (one way) cross-country ramble through thick sedges and grasses along the canal’s edge. Because the eastern edge of Big Marsh transforms from a wet marsh in spring to a mostly dry marsh by late summer (with water levels falling 2’-3’), August and September are likely the best months to take this hike. Not only will the mosquitoes be less intense, but hikers will have the best chance for dry marsh underfoot while exploring. In any season, one should bring plenty of insect repellent, plus keep an eye out for sinkholes and deep channels hidden in the dense marsh vegetation.

The hike starts at the new gravel parking area and goes cross country to the west through the forested meadow (see Hiking Map download below). Within 100 yards, one comes to an old rotted boardwalk (caution!) next to the big 1940s drainage canal. The route then follows the edge of this old canal south and west, with close-up views of the ditch restoration project in progress. Look for otters, herons and spotted frogs in the ponds, plus sandhill cranes and soaring hawks out on the open marshlands.

At 0.9 miles, one can walk across plugs in the old drainage canal and hike north through dry marsh to several older restoration ponds that are potential overwintering sites for spotted frogs, with expansive views across Big Marsh. Another 0.3 miles to the southwest, the cross-country route comes to the banks of Big Marsh Creek, which can make a good hike destination. If the mosquitoes are too bothersome, one can retreat south into the fir forests here for a shady rest and lunch break.

For detailed driving directions to the hike at Big Marsh, see the Road Map download below.

Download (PDF, 844 KB): Photos of the Big Marsh Hike
Download (PDF, 501 KB): Road Map for Big Marsh Hike
Download (PDF, 657 KB): Hiking Map for Big Marsh

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.