Discovery Park (Seattle): Natural History

  • By David B. Williams
  • Posted 12/16/2015
  • Essay 11161

With 534 acres of forest, meadow, and beach on a broad point projecting into Puget Sound, Discovery Park at West Point in Seattle's Magnolia neighborhood is the city's largest green space and among its most fascinating geologically and ecologically. Nowhere in the city can one see a better example of sediments deposited during the most recent ice age and the beach includes sediments from one of the few tsunamis known in Puget Sound. Archaeological evidence provides insights into how Native Americans responded to dramatic geological changes. Ecologically the park habitat is unusual because although native trees cover much of its area they are not the region's typical Douglas fir, western red cedar, and western hemlock. That trio does occur but nowhere as abundantly as red alder and bigleaf maple. Early surveyors described a forest dominated by fir, cedar, and hemlock, but land-clearing, especially after establishment of Fort Lawton on the site in the 1890s, removed much of it. As military use declined, allowing creation of Discovery Park in the 1970s, maple and alder moved into disturbed areas. So did invasive non-native plants, prompting ongoing efforts to replace them with native vegetation. Even some long-unseen animals have recently reappeared.


During the past two million years or so, at least five major advances of glaciers have pushed out of the north into the Seattle region. The last glacier was a 3,000-foot-thick ice mass known as the Puget Lobe of the Cordilleran Ice Sheet (one of two huge sheets of ice that covered North America), which spread as far south as Olympia before retreating, or melting, back to the north. Most people refer to this period of glaciation as the last ice age, though geologists call it the last glacial maximum.

Only the final advance, when the Puget Lobe crossed into the Seattle region 17,400 years ago, left behind evidence in Seattle that still remains, though one can find deposits from the period before the ice reached here. Earlier sediments have either been buried or been removed during subsequent glaciations. No place in Seattle is better than the South Bluff at Discovery Park to see the remaining deposits, which comprise four layers within the park.

Olympia beds: The brownish, layered rocks at the bottom of the bluff were deposited on a floodplain and in lakes during what is known as an interglacial, the most recent of which was between 60,000 and 20,000 years before present. The environment during this period was probably similar to today's with forests, streams, and lakes, though we have no evidence of any feature such as Puget Sound. What we have, though, are fossils from large mammals, such as giant ground sloths (the size of a VW Beetle), Columbia mammoths, and mastodons, that roamed the forests and plains. Geologists have dated pieces of wood within the Olympia beds at between 22,400 and 18,100 years ago.

Lawton Clay: Directly atop these beds sit fine layers of dark gray clay and light gray silt. They are the first layers deposited during the last ice age. Deposition occurred when the Puget Lobe formed a dam that created a large lake in the Puget lowlands. The Lawton Clay is the fine-grained sediment that rivers and streams transported into the lake. At Discovery Park the Lawton Clay is 82 feet thick but it is as much as 100 feet thick in other spots. Within this layer are boulders, up to 10 feet across, called dropstones, which were left when rafts of boulder-strewn ice floated into the lake, melted, and dropped their loads.

Esperance Sand: As the Puget Lobe approached the Seattle area, streams washing out of the ice front deposited sand, silt, and gravel, which form the Esperance Sand. It tends to be lighter in color than the Lawton and is up to 200 feet thick. Geologists refer to this type of deposits as advance outwash.

Vashon Till: Finally, the ice arrived and deposited the ground-up landscape of silt, sand, cobbles, pebbles, and boulders. The layer is locally known as hardpan and is up to 30 feet thick. It is the highest, or youngest, layer of glacial sediment at West Point, and tops most Seattle hills though not all of them. But it is not always present; for example it is not everywhere in the park.

Another key geological feature visible at Discovery Park is landslides. They occur here and across Seattle because of the differences between the Lawton Clay and Esperance Sand. When it rains or snows, water percolates down into the Esperance, which is a porous layer, until it reaches the Lawton, which is basically impervious because of the fine-grained clay. The water then flows atop the clay layer, following gravity downhill and emerging at lower elevations as seeps and springs. This process weakens the contact between the clay and sand and makes the slope susceptible to sliding, which can be seen clearly at South Bluff. A 1994 study found that the bluff at Discovery Park retreats as much as 80 feet per century.

From a geological and ecological point of view, landslides are important to the beaches below the bluffs. The slides provide much-needed sediment that helps in building beaches and spits. Wave action also makes bluffs unstable by undercutting the base. At Discovery Park, waves more often come from the north, though the South Beach area receives greater wave energy, which results in the sandy beach that emerges at low tide.

The interaction between waves, sediments, and erosion is well-illustrated by changes at West Point over the past several thousand years. Archaeological and geological evidence shows that around 4,000 years ago people seasonally visited rocky shores, where they gathered mussels and periwinkles. They also hunted elk and deer in the uplands, as well as the occasional seal. By 3,000 years ago, the local diet had changed as landslides had created a sandier beach more conducive to clams. Over time landslides led to the formation of a lagoon, which provided additional habitat for shellfish. And then about 1,100 years ago a massive earthquake in Puget Sound caused a tsunami that buried the beach area in silt and sand. During the earthquake the beach subsided some three feet, which made the habitable region much smaller. Despite the dramatic change the Indian peoples of the region quickly returned to and made use of the beach, though they would have used slightly higher landforms.

Early Records of Plant Life

The earliest details of plant life in what is now Discovery Park come from archaeological evidence unearthed near the Metro wastewater-treatment plant built at West Point in the 1960s. Douglas fir, western red cedar, red alder, and western hemlock were the most abundant woody tree fossils. Archaeologists hypothesized that conifers were probably used as fuel, whereas the alder, as well as maple, elderberry, and ocean-spray, were either used as fuel or for skewers and/or racks, though the latter two burn slowly, which may indicate their use for smoking meat. Other plants include hazelnut, bitter cherry, and mock orange. All of the species found in the archaeological digs still grow in the park. The report on the digs concludes that "the number and diversity of plant taxa in the botanical assemblage remained relatively constant during the 4,000 years of occupation of the West Point site, suggesting a long period of plant subsistence" (Larson and Lewarch, 13-34).

The oldest contemporary written records of the area's botany are the notes of the federal Government Land Office's (GLO) Cadastral Surveys of 1855. GLO surveyors worked across the entire continental United States west of Ohio. The goal of the surveys was to delineate the land and establish the boundaries of the township and range system, which could be used to identify parcels of land in order to record ownership. Surveys divided the land into six-by-six-mile units, or "townships." These 36-square-mile townships were subdivided into 36 one-square-mile "sections." At each section and quarter-section, surveyors blazed two or four trees as "witness" or "bearing trees." In order to accomplish this task, teams went out on the land, walked boundaries between sections, and noted native vegetation, topography, locations of fire or other disturbance, vegetation communities, and general soil types.

On October 10, 1855, GLO surveyors David Phillips and William A. Strickler passed through the future Discovery Park. The landscape above the bluffs, which would later form the main part of the park, looked like most of the area around Seattle. The surveyors described the land as hilly with first- and second-rate soil and a forest of Douglas fir, western hemlock, western red cedar, red alder, and maple (most likely bigleaf maple, though they were not specific). The firs were large, up to 65 inches in diameter, but not unusually so compared to other areas they had surveyed. Where they noted the understory, which was not consistent, it included young hemlock, fern (no species given but sword ferns are Seattle's most common fern species), and salmonberry.

Throughout the Puget lowland, western hemlock and western red cedar are the climax forest species, meaning that in a mature forest those will be the dominant trees. In a younger forest Douglas fir would predominate as a successional species. The fact that the surveyors found young hemlock is a sign that the Discovery Park forest was "beginning to take on the characteristics of an older forest" (Larson, 134).

Below the bluff was a "tide prairie" devoid of trees, which was similar to that found at other "points" in Seattle, such as Alki Point, Brace Point (south of the Fauntleroy ferry dock), and Meadow Point (Golden Gardens). Because these points jutted out into the sound they were buffeted by high winds. They also tended to be sandy. Near the end of the nineteenth century botanists collected 58 native species that ended up at the University of Washington Herbarium. They included rose-colored Hooker's onion, golden paintbrush, lilac-to-pink saucer clover, white prairie star, and violet harvest lily, none of which now grow in Seattle. Indeed, of the original 58 an additional 19 have been extirpated and 16 more are considered rare or uncommon, according to botanist Arthur Lee Jacobson.

What the surveyors did not note at the future Discovery Park, except in one case, was the vegetation of any wet areas such as seeps, springs, wetlands, or creeks, because it wasn't their job to do so unless they passed directly through a such a site. Much as would be found across Seattle's historic landscape, wetter areas would have dotted the area with a host of plants adapted to moister conditions. These would include shrubs and herbaceous plants such as skunk cabbage, horsetail, bigleaf avens, lady fern, deer fern, salmonberry, and devil's club.

One other feature would have been the steep landslide-prone bluffs that rose out of Puget Sound. Red alders and bigleaf maples, which botanists consider as pioneer species, along with an understory of stinking nettle, fringe cup, and horsetail, would have colonized the disturbed lands, though the plants lived on a sort of conveyor belt of constant change: landslide, colonize, grow, repeat.

Changes to the Ecosystem

The ecosystem encountered by Phillips and Strickler began to change soon after newly arriving settlers made land claims in the area. In order to establish themselves and build homes, they logged the land, carving out space for potential homes and roads. After the United States government began to acquire the property in 1896 for an army post that became Fort Lawton, workers stepped up the process of forest alteration. "All but ornamental shade trees were removed by the contractor's crews" (Boyle and Fürész, sec. 8, p. 9). By 1898, almost 100 acres had been cleared for a parade ground, housing, roads, and other uses, such as an open pasture for horses. (In 1910, there were at least 500 stabled at the base.)

A 1910 report by landscape architect John Charles Olmsted (1852-1920) noted that after loggers had removed most of the large timber "twenty or thirty years ago," fire had consumed "smaller dead wood and trimmings" (Olmsted to Miller). In addition, alders had replaced the conifers, although Douglas fir trees up to 250 feet tall still remained. There was also a dense understory, which made the woods "practically impassable" (Olmsted to Miller). Olmsted recommended selective cutting.

The early twenty-first century forest community reflects the previous century and a half of use. Deciduous trees, rather than conifers, now dominate with a forest of red alders and bigleaf maples covering most of the park. Variation does occur and conifers still persist but what had once been a forest of perpetually green trees that did not annually lose their foliage is now a landscape where colors change through the year, leaves drop, and trees are often as broad as they are tall.

Several factors influence variation, including microhabitat, time since and degree of disturbance, and introduction of non-native species. In particular, the amount of available water is the primary environmental control. For example, Vashon Till close to the surface near the North Bluff (west of the north parking lot) results in a high water table that fosters the growth of Sitka willow. Other moisture-rich locales, some formed by the construction of roads and parking lots (the north parking lot is a prime example) support classic wetland species such as horsetail and skunk cabbage.

In contrast, two drier areas support a much different contingent of plants. One is the park's most unusual ecosystem, the dune fields above the South Bluff and west of the Parade Ground. Their formation is probably a two-part process, though no one has studied them thoroughly. The Esperance Sand layer extends all the way up to the bluff in this location. When it weathers it generates sand; additional sand could also come from wind transporting eroded sand into the meadow from the bluffs to the west. Then, after the area's original forest was cleared, this area became more sandy because of human use. Continued human use keeps the area sandy.

During the era of Fort Lawton and the early years of Discovery Park, non-native grasses and shrubs, such as Scotch broom, invaded the dunes. Restoration work in subsequent years achieved the removal of the broom but few native species have returned and "nary a native" grows there, as one botanist has said (Antieau interview). Restoration is an on-going process throughout the park, though it is hampered by soils that were hammered over the decades by intense human use, which has obliterated the soil food web of microorganisms and micorrhizae.

The other dry habitat community is the area where madrona trees grow, on the park's southern boundary. Curiously, madronas are the plant that gave the Magnolia neighborhood its name. In 1856 Lieutenant George Davidson of the United States Coast and Geodetic Survey mistook the bluff's madronas for magnolias and we have been stuck with the error ever since.

The maple-alder forest that covers much of the park reflects how these native trees colonize disturbed habitat and grow quickly. Bigleaf maples live longer and grow larger than alders, though alders grow faster and can reach heights of 80 feet in two decades. Alders are short-lived trees, rarely living more than a century. They have gray, birch-like bark often covered in mosses and lichens and in spring produce catkins that spread abundant pollen. Bigleaf maples can live for up to 200 years, grow up to 100 feet tall, and produce huge leaves, some up to two feet wide, that turn brilliant yellow in fall. Licorice ferns, mosses, and lichens commonly grow on trunks and branches.

Plant Restoration

Efforts to restore the land to its former habitat, or at least to promote native over non-native plant species, have been a central focus during the decades since the park became city property, with a total of more than 50 separate projects. One of the best-documented involved a 13-acre site extending northeast from the Parade meadow toward Illinois Avenue and was coordinated primarily by volunteers Tom Palm and Phil Vogelzang. The site included the base's hospital and headquarters, barracks, and theater, along with several roads. By the late 1980s, all buildings and most of the smaller roads had been removed. Final road removal took place in 2001, though the main Discovery Park road curves through the area.

As happens in many disturbed landscapes around Seattle, Scotch broom and Himalayan blackberry moved in and took over the grounds after building removal. They were also the first plants to be removed in the restoration, which required mowing, hand cutting, rootball removal, and plant pulling, followed by raking the debris into composting piles and berms. Crews then planted native trees and shrubs, supplemented by native ground cover, depending upon soil type. For example, a former grassy slope was planted with Douglas fir, Pacific ninebark, black hawthorn, black twinberry, mock orange, red-flowering currant, tall Oregon grape, quaking aspen, Indian plum, and sword fern. An area previously covered in blackberry now features a berm, above which are red-flower currant, red-osier dogwood, Douglas spirea, snowberry, and a number of sand-loving wildflowers and some Idaho fescue bunchgrass.

Animals at Discovery Park

As with plants, the earliest evidence of animal species comes from archaeological digs along the beach at West Point. By far the most abundant mammal remains are deer, followed by elk, both of which were important food sources for the people who lived in the area. Other remains include black bear, bobcat, mountain beaver, beaver, and raccoon, as well as dolphin and harbor seals. The evidence shows that during the earliest period of known habitation (4,500 to 3,550 years before present) people ate the larger mammals, but over the next 700 years or so they preferentially consumed the smaller mammals. No evidence was found that reveals why this change occurred but it could reflect differences in how and when people used the site.

Curiously, several of these animals of yore have reappeared in the park. In 2009 visitors saw a 140-pound cougar, which wildlife officials trapped and released elsewhere. The same year residents just north of the park reported a black bear. It then apparently headed north. More common are coyotes, which live throughout the park.

The park is best known for its bird population, which is the most diverse of any park in the city with more than 270 species, ranging from bushtits to barn owls, both of which nest in the park. (There is speculation that the owls nest in old pipes in the bluffs. Kingfishers also nest in the bluffs but in one- to eight-foot-long holes excavated into the sandy banks.) The reason for the diversity is simple; the park has both saltwater beaches and an extensive upland area of forest and meadow. In addition, because the park juts out into Puget Sound it acts as a magnet attracting migratory birds, such as Steller's jays. The bluffs also provide a location for birds of prey, such as bald eagles and osprey, which take advantage of the updrafts to soar.

Discovery Park has functioned as a research lab for more than 25 years. University of Washington biologist Michael Beecher and his students have studied how and why song sparrows communicate. The small russet-and-gray birds with streaked white chests flit about open habitat and are a common bird in the park. Many have small bands on their legs, which Beecher and his students have attached to help distinguish individual birds. The biologists found that a male song sparrow will initially respond to a threat from another male entering its territory by repeating the intruder's song. If the bird wants to acknowledge the threat but not threaten the intruder, it will sing a song that both birds know. If the threat doesn't work, the threatened bird flies in closer and waves its wings, sort of equivalent to "flipping the bird" (McElroy). If that fails, an attack on the "trespasser" follows. "This is one of the most complicated communication systems outside of human language," according to ÇaÄŸlar Akçay, who studied the behavior as a graduate student working with Beecher (McElroy).

Sources: Richard Galster et al., "Engineering Geology of Seattle and Vicinity," in Geologic Field Trips in the Pacific Northwest, vol. 2, ed. by Donald Swanson and Ralph Haugerud (Seattle: University of Washington, 1994), 2D-3; Kathy Goetz Troost and Derek B. Booth, "Geology of Seattle and the Seattle Area, Washington," in Landslides and Engineering Geology of the Seattle, Washington, Area ed. by Rex Baum, Jonathan W. Godt, and Lynn M. Highland (Boulder, CO: Geological Society of America, 2008), 1-35; John Charles Olmsted to Colonel S. W. Miller, July 5, 1910, pp. 16, 17, Job 2720, Reel 97, MSS52571, Olmsted Associates Records, Library of Congress, Manuscript Collection, Washington, D.C.; Raymond Larson, "The Flora of Seattle in 1850: Major Species and Landscapes Prior to Urban Development" (master's thesis, University of Washington, 2005), 134, 135; The Archaeology of West Point, Seattle, Washington: 4,000 Years of Hunter-Fisher-Gatherer Land Use in Southern Puget Sound ed. by Lynn L. Larson and Dennis E. Lewarch (Seattle: Larson Anthropological/Archaeological Services, 1995), 2-27, 2-63, 13-34, 13-36; Richard S. Fleming et al., Discovery Park Inventory and Natural History Report (Seattle: University of Washington, Institute for Environmental Studies, 1974), 48; Susan Boyle and Sonja Sokol Fürész, Fort Lawton National Register of Historic Places Nomination Form, August 13, 2007, copy available at Seattle Department of Neighborhoods website accessed December 15, 2015 ( HistoricDistricts/FortLawton/FortLawton-National-Register-Nomination.pdf); Lornet Turnbull and Christine Clarridge, "Discovery Park Cat Gets Treed and Freed: 140-pound Male Cougar 'Sweetheart' After Capture," The Seattle Times, September 7, 2009, p. A-1; "Black Bear Sightings Near Discovery Park," May 17, 2009, Magnolia Voice website accessed December 9, 2015 (; Discovery Park Habitat website accessed December 9, 2015 (; Molly McElroy, "Get Off My Lawn: Song Sparrows Escalate Territorial Threats," February 12, 2013, University of Washington News and Information website accessed December 9, 2015  (; David Williams interview with Clay Antieau, November 24, 2015, Seattle, notes in possession of David Williams, Seattle, Washington; Arthur Lee Jacobson, email to David Williams, November 7, 2002, in possession of David Williams; Kathy Troost, email to David Williams, November 28, 2015, in possession of David Williams.

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