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Marys Peak: The Oregon Coast Range’s Sky Island

Articles: Marys Peak: The Oregon Coast Range’s Sky Island

Spring 2024 

Sky islands are peaks that are significantly higher in elevation than the surrounding environs. Striking examples can be found in the Desert Southwest, where peaks thousands of feet higher than the surrounding desert can have life zones that range from the hot desert floor to spruce-pine forests that would be much more at home in the Far North. These peaks can serve as biological refugia for species that have, in effect, been “stranded” by the changing climate since the last Ice Age. Ascending these mountains, one travels through these distinct life zones on the way to the summits. The change in elevation from the bases to the tops of these peaks can bring a difference in temperature by as much as 30°F (-1°C) in the summer.

Allium crenulatum, the Olympic onion, grows on talus slopes across the Pacific Northwest. Photo: Merrill Jensen
Marine sediments laid down over the course of millions of years ago. Photo: Merrill Jensen

A prime example of this is Marys Peak, the tallest point in the Coast Range in Oregon. At 4,097 feet (1,249 meters), it stands 500 feet taller than all the surrounding summits that are adjacent to the Pacific shore. On a clear day from the top, one can look to the west and see breakers on the coast, and then, looking to the east, a parade of 13 of the Cascade volcanoes. Between the peak and the Cascades, the broad, fertile Willamette Valley spreads out like a carpet where diversified agriculture produces more than 170 different crops. Grass seed, wine grapes, hazelnuts, ornamental nursery plants, Christmas trees, and numerous vegetable and berry crops make for an agricultural tapestry rarely seen anyplace else. The view from the summit also provides a chance to visualize when the great Ice Age Missoula floods covered the valley floor with waters up to 300 feet (91 meters) deep. Those floods brought sediments that enriched the soils, leading to the agricultural bounty for which the Willamette Valley is noted.

The geology that makes Marys Peak unique started 55 million years ago with magma eruptions on the ocean floor off the west coast of what would eventually become North America as we know it now. When basalt erupts underwater, it forms into distinctive pillow-shaped flows which geologists can identify as oceanic in origin. There is a rock quarry on the peak located at approximately 2,700 feet (823 meters) that has some of the best examples in the world of this phenomenon.

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For millennia, erosion from coastal areas laid down multiple layers of sediments consisting of sand and siltstone. These layers can be seen on the drive to the summit. Approximately 40 million years ago, the eastward-drifting Juan de Fuca Plate that subsides under the westward-drifting North American Plate created uplift along the coast and started pushing up the Coast Range as seafloor was scraped off the subducting tectonic plate. This subduction process produced magma that intruded into the older basalts and sedimentary layers to form sills (horizontal layers of igneous rock that form between preexisting layers of rock) of harder, erosion-resistant rock. It is estimated that thousands of feet of softer sedimentary rock has eroded from the peak to the resistant basalt layer—called gabbro—that forms the top of the peak. This cap of gabbro has allowed Marys Peak to stand taller than the surrounding range. As one drives to the summit, examples of all this 55-million-year-old geology are laid bare for one to observe.

Marys Peak is botanically notable due to its location in the Coast Range, to the point that the Siuslaw National Forest established the Marys Peak Scenic Botanical Special Interest Area (SBSIA). This is partly due to its scenic and recreational values just 15 miles (24 kilometers) southwest of Corvallis. Primarily, this special designation is due to the diverse plant communities that occupy the slopes and summit area. Over the years, botanists have tallied more than 200 species of plants. There are three major plant habitats that occupy the mountain: forest, meadow, and xeric rock garden. 

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The Willamette River flows to the north through the entire length and is surrounded by mountains on three sides: the Cascades, the Coast Range, and the Calapooya Mountains. The valley’s fertile, alluvial soils and flat topography attracted settlers of European origin after being touted as the land of “milk and honey” in the early 1800s.

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The xeric communities grow on the exposed southern summit where the soils are thin and gravelly. It rarely rains in the summer (less than 5 percent of the annual precipitation), and in the winter, hurricane-force winds blow the snow off this section of the mountain, creating an extremely dry microclimate. Botanists hypothesize that this plant community is a relic from a warm, dry period of 4,000 to 6,000 years ago. The “rock garden” community of subalpine plants is one of the most beautiful sites on the summit. Hikers are treated in the spring to profuse blooms of spreading phlox (Phlox diffusa), Cascade desert parsley (Lomatium martindalei), harsh paintbrush (Castilleja hispida), and Cardwell’s penstemon (Penstemon cardwellii).

A very fine example of pillow lava that forms during eruptions under the ocean. These are located at approximately 2700' elevation on the Peak. Photo: Merrill Jensen
A closer view of the rock gardens that grace the summit area. Photo: Merrill Jensen

As the climate cooled, plants that are more adapted to higher, cooler locales (such as the peaks in the Cascades) are evident in the noble fir (Abies procera) forest that occupies an area just off the summit. Deep snow accumulates with drifts up to 10 feet (3 meters) in this zone, which allows a completely different flora to thrive just downhill from the xeric zone of the summit. Trees in this section of forest range from 150 to 250 years old. This is one of the few locations within its range where noble fir forms an almost pure stand.

Lower down the mountain, the forest changes to mixed Douglas fir (Pseudostuga menziesii) and western hemlock (Tsuga heterophylla). The trees on the lower slopes have been subject to fires and logging, and therefore are younger. Some old-growth Douglas fir can be found in the valleys where logging was impractical. Some salvage logging of noble fir was permitted to remove windthrown trees in the visitor-use summit area.

The Fibonacci Sequence expressed in the new growth of Abies procera, the Noble Fir. Photo: Merrill Jensen

The meadow communities surround the summit area where moisture levels are higher and allow the growth of grasses and sedges (Festuca sp., Agrostris sp., and Carex sp.). Mingled across the meadows are extensive stands of tiger lily (Lilium columbium) that form large patches of orange in summer. In areas that receive deeper winter snows, drifts of glacier lily (Erythronium grandiflorum) start to bloom as the snows retreat and give an early spring show. Other wildflowers that grace these areas surrounding the summit and add to the breathtaking spring and early summer show include Menzies larkspur (Delphinium menziesii), sicklekeel lupine (Lupinus albicaulis), blue field gilia (Gilia capitata), Western wooly sunflower (Eriophyllum lanatum), and Oregon iris (Iris tenax).

The meadow communities have been shrinking due to the encroachment of noble fir; this has been observed in other areas around the Pacific Northwest over the past century. Researchers speculate there are two possible causes for tree encroachment, both are related to practices on the landscape that fell out of favor. Fire was and remains a tool utilized all across North America by Indigenous Peoples to maintain a healthy ecosystem.

While cultural burning remains an important part of land management, authorities prohibited the practice on public lands for many years alongside other fire suppression policies. Additionally, livestock grazing, which was associated with non-native settlement, no longer occurs. The US Forest Service, Bureau of Land Management, and volunteer groups are removing small trees to restore the meadows to what is believed to be pre-settlement size.

Marys Peak is easily accessible by car, although the road is not maintained in winter. Snowstorms on the higher reaches frequently make the road impassable, even for four-wheel-drive vehicles. There are easy trails on which one can roam different parts of the mountain—as well as trails that ascend from different locations at the base of the mountain, for those looking for a more energetic hike.

Erythronium grandiflorum, avalanche or glacier lily blooms early in the spring. Photo: Merrill Jensen

The best times to view the floral display are scattered across the calendar. The first is late spring as the summit snows retreat. This is generally from early May to late June and is the best time to catch the short bloom period of the glacier lilies. Next is from late June through mid-July, when the meadows reach their peak flowering. Later in July, the tiger lilies are at their best, however that can be dependent on earlier spring conditions and deer populations. Nice spring weather brings deer herds to the higher meadows earlier in the season where they can graze on the lily buds. Wet, windy weather will keep the deer lower on the mountain where they shelter in the forest.

Marys Peak, the Oregon Coast Range's Sky Island. Photo: Merrill Jensen
Looking northwest across the Noble Fir forest, one can see the Pacific Ocean. Photo: Merrill Jensen

When visiting, one needs to plan for changeable weather conditions. The peak’s proximity to the Pacific Ocean can bring high winds and lower temperatures. One should come prepared with appropriate rain gear, layers of warm clothing, waterproof footwear, and food and water.

The summit parking lot is a Forest Service day-use fee area ($5 per vehicle or valid recreation pass). Facilities are limited and there is no water available. Information panels cover the flora, fauna, and history of the area. Sunny weekend weather can bring large numbers of people to the peak and can cause congestion at the day-use parking area. Besides offering stunning views of the surrounding area, it is also a perfect spot for stargazing on clear summer evenings.

A view across the rock gardens that grace the summit area. Photo: Merrill Jensen
Achlys triphylla is a forest denizen that blooms on the lower slopes of the Peak. Photo: Merrill Jensen

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Resources

Visiting Mary’s Peak and the Siuslaw National Forest. USDA,gov

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