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<title>Tryon Creek</title>
<authors>Wikipedia</authors>
<publisher>wikipedia.org</publisher>
<publishedplace>network</publishedplace>
<publishedyear>2010</publishedyear>
<edition></edition>
<category>Culverts</category>
<section id="43072" fatherid="0" title="" lv="" priority="-1" level="1">
Tryon Creek is a  tributary of the Willamette River in the U.S. state of Oregon. Part of the drainage basin of the Columbia River, its watershed covers about  in Multnomah and Clackamas counties. The stream flows southeast from the Tualatin Mountains (West Hills) through the Multnomah Village neighborhood of Portland and the Tryon Creek State Natural Area to the Willamette in the city of Lake Oswego. Parks and open spaces cover about 21 percent of the watershed, while single-family homes dominate most of the remainder. The largest of the parks is the state natural area, which straddles the border between the two cities and counties.
The bedrock under the watershed includes part of the last exotic terrane, a chain of seamounts, acquired by the North American Plate as it moved west during the Eocene. Known as the Waverly Hills Formation, it lies buried under ash and lava from later volcanic eruptions, sediments from flooding and erosion, and layers of wind-blown silt. Two dormant volcanoes from the Boring Lava Field are in the Tryon Creek watershed.
Named for mid-19th century settler, Socrates Hotchkiss Tryon, Sr., the creek ran through forests of cedar and fir that were later logged by the Oregon Iron Company and others through the mid-20th century. Efforts to establish a large park in the watershed began in the 1950s and succeeded in 1975 when the state park was formally established. As of 2005, about 37 percent of the watershed was wooded and supported more than 60 species of birds as well as small mammals, amphibians, and fish. At the same time, the human population was about 18,000.

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<section id="43073" fatherid="0" title="Course" lv="" priority="-2" level="1">
<section id="43074" fatherid="43073" title="" lv="" priority="-1" level="2">
Tryon Creek begins slightly north of Interstate 5 (I-5) and Oregon Route 99W near Multnomah Village and flows southeast for Although other sources give the creek's length as , Chapter 10 of Fanno and Tryon Creeks Watershed Management Plan by the Portland Bureau of Environmental Services gives a precise length of . The plan describes inflow above that point as a "headwaters complex" that "includes all small upper tributaries above RM 4.85." By convention, stream lengths do not include tributary lengths.  through Portland residential neighborhoods as well as Marshall Park and the Tryon Creek State Natural Area to its confluence with the Willamette River in the city of Lake Oswego. Not far from its source, the main stem runs through three closely-spaced culverts with a combined length of  then flows on the surface before entering another culvert,  long under Southwest 30th Avenue at river mile (RM) 4.56 or river kilometer (RK) 7.34. Shortly thereafter, the stream passes under Route 99W (Barbur Boulevard) and I-5 through another culvert,  long.Portland Bureau of Environmental Services, Chapter 10, pp. 1-7
Tryon Creek receives Falling Creek from the  at  from the mouth. Quail and Burlingame creeks enter from the  shortly thereafter. At Marshall Park, the stream passes through a series of rock pools and steps known as the Marshall Cascade from RM 3.48 (RK 5.60) to RM 3.28 (RK 5.28). Arnold Creek, which is Tryon Creek's largest tributary, enters from the   from the mouth. Almost immediately, the creek enters a culvert, about  long, that passes under Southwest Boones Ferry Road.
Shortly thereafter, Tryon Creek enters the Tryon Creek State Natural Area. To the stream's  is the North Creek Trail. Soon the creek receives Fourth Avenue Creek from the . At this point, the Fourth Avenue Trail runs parallel to the creek along the  bank. This trail soon merges with the Lewis and Clark Trail, which also runs parallel to the creek along the  bank. Then Tryon Creek passes under the High Bridge, the uppermost of five footbridges that span the main stem within the park. High Bridge carries the Middle Creek Trail as well as a linear horse trail connecting the park's North and South horse loops. Below this bridge, the creek flows for about  before passing under the Beaver Bridge. In this stretch, the Middle Creek Trail parallels the stream along the  bank but crosses to the  bank at the bridge. Shortly thereafter, the creek passes under Obie's Bridge, which carries the Old Man Trail.

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<section id="43075" fatherid="43073" title="Discharge" lv="" priority="-2" level="2">
Since 2002, the USGS has monitored the flow of Tryon Creek at a station  from the mouth. The average flow between then and 2007 was . This is from a drainage area of , about 97 percent of the total Tryon Creek watershed. The maximum flow recorded during this period was  on December 13, 2003. The minimum was  on September 4, 5, and 12, 2002.
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</section>
<section id="43076" fatherid="0" title="Geology" lv="" priority="-3" level="1">
Between 15 and 16 million years ago, in the Middle Miocene, eruptions of Columbia River basalts from volcanic vents in eastern Oregon and Washington flowed across much of northern Oregon, sometimes reaching the Pacific Ocean.Bishop, pp. 144-48 Although these basalts have been mapped in the West Hills under Marquam Hill, Hoyt Arboretum, and the steepest slopes of Forest Park, they flowed around but did not completely cover the Waverly Hills Formation in the Tryon Creek watershed.
Starting about 3 million years ago and continuing at least through the late Pleistocene, extensional faulting of the Earth's crust led to eruption of small volcanoes in the Boring volcanic field. This field extended roughly from Portland and Tualatin on the west to Battle Ground, Washington, on the north to Sandy and Boring on the east.Bishop, pp. 192-93 Two of these volcanoes, Mount Sylvania and Cook's Butte, are in the Tryon Creek watershed. The Mount Sylvania eruptions included ash plumes and lava flows that covered some of the Waverly Heights Formation and Columbia River basalts.
About 15,000 years ago, cataclysmic ice age events known as the Missoula Floods or Bretz Floods originating in the Clark Fork region of northern Idaho inundated the Columbia River basin many times. These floods deposited huge amounts of debris and sediment and created new floodplains in the Willamette Valley. Over long stretches of time between the great floods, dry winds deposited silt. At elevations above  in the Tryon Creek watershed, wind-blown silt covers the lava, while at lower elevations sand and gravel cover the bedrock.

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<section id="43077" fatherid="0" title="Watershed" lv="" priority="4" level="1">
<section id="43078" fatherid="43077" title="" lv="" priority="-1" level="2">
About  of precipitation, almost entirely rain, fall on the watershed each year. Summers are dry, and most of the precipitation occurs between October and May. Elevations within the drainage basin vary from Mount Sylvania, which rises to  above sea level  in the West Hills, to  where the creek enters the Willamette River. Between 60 and 75 percent of the slopes in the watershed exceed a 30-percent grade and are especially steep near the headwaters. Impervious surfaces cover about 24 percent of the basin. These surfaces and the relatively impermeable silt and clay soils that underlie the area contribute to rapid runoff and low baseflows in the creek and its tributaries. The total length of surface streams in the drainage basin is about , while another  run through culverts or pipes.Portland Bureau of Environmental Services, Chapter 2, pp. 5-9 Although major flooding in 1996 caused landslides and severe damage to stream beds and banks along Tryon Creek and its tributaries, it caused no significant property damage in the watershed.Portland Bureau of Environmental Services, Chapter 2, pp. 16-17
In 2000, the population of the Tryon Creek watershed within Portland was about 18,000. In 2005, Portland's Bureau of Environmental Services (BES) described land-use zoning in the watershed as follows: single-family residential, 55 percent; parks and open space, 14 percent; multi-family residential, 5 percent; commercial, 3 percent, and insufficient data, 2 percent. To reach 100 percent, BES listed but did not differentiate by zoning type the roughly 20 percent of the watershed that lies beyond the Portland city limits. Metro, the regional government for the Portland metropolitan area, says that parks and natural areas cover about 21 percent of the total watershed, while single-family housing dominates most of the rest.

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<section id="43079" fatherid="43077" title="Tributaries" lv="" priority="2" level="2">
The major smaller streams in the Tryon Creek watershed are Arnold Creek and Falling Creek. The larger of the two, Arnold Creek, has a watershed of roughly  or 18 percent of the  total, while Falling Creek's watershed covers  or 6 percent of the total. The seven named tributaries from mouth to source are Nettle, Palatine Hill, Red Fox, Park, Fourth Avenue, Arnold, and Falling creeks.
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<section id="43080" fatherid="43077" title="Water quality" lv="" priority="3" level="2">
BES monitors water quality at three Tryon Creek sites. Two are near I-5 and Barbur Boulevard in the upper watershed, and the third is at Southwest Boones Ferry Road, about  from the mouth. BES looks at several indicators such as dissolved oxygen, nutrients, and total suspended solids. Diffuse pollution from nonpoint sources enters the creek from its urban surroundings. Point sources of pollution in the creek include two major upper-watershed stormwater outfalls draining  of the upper watershed and contributing about half of the creek's total suspended solids. As of 2004, the only water-quality indicator in the watershed that failed to meet minimal standards was the water temperature.Portland Bureau of Environmental Services, Chapter 6, pp. 2-7
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<section id="43081" fatherid="0" title="History" lv="" priority="-5" level="1">
In 1850, Socrates Hotchkiss Tryon, Sr., a pioneer settler of European descent, established a donation land claim at the south end of Tryon Creek canyon. Five years later, he died, leaving the land to his wife, Frances. The land then passed to other relatives, including Socrates Tryon, Jr., who sold the  in 1874 to the Oregon Iron Company. For nearly 25 years, the company cut virgin cedar and fir to use in its foundry in Lake Oswego. Its logging road later became Old Iron Mountain Trail in the Tryon Creek State Natural Area. In 1900, fire in the upper canyon  charred snags still visible along the natural area's Center and Big Fir trails.
Logging resumed in 1912 in the north part of the canyon, where The Boone's Ferry Wood and Tie Company had a site near what became Alfred Street. A sawmill and steam donkey engine operated near the future sites of Beaver Bridge and Obie's Bridge. The lumber was used chiefly for railroad ties, cordwood and flagpoles, and  huge cedar stumps that remain in the park. Intermittent logging continued through 1961, and a 1962 windstorm known as the Columbus Day Storm blew down many remaining trees.
Local efforts began in the 1950s to establish a park along the creek, In 1969, the government of Multnomah County bought  to start a large regional park and sought citizen assistance with the project. This led to formation of Friends of Tryon Creek Park, which raised funds, helped arrange land deals, worked on problems of jurisdiction in a two-county, two-city park, and sought help from the state. In 1970, Oregon Governor Tom McCall announced the formation of Tryon Creek State Park.
Over the next few years, the state bought more than  of land for nearly $3 million, including federal matching funds. The Friends and the state collaborated in park planning and further fund-raising. In 1973, more than 300 volunteers built trails, and the nature center and shelter were finished by 1975. The park was officially dedicated on July 1, 1975 and later re-named Tryon Creek State Natural Area.

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<section id="43082" fatherid="0" title="Vegetation and wildlife" lv="" priority="6" level="1">
Riparian zones and floodplains are relatively intact along the lower reaches of the main stem in the state natural area, fairly intact in Marshall Park, and marginal in the upper reaches surrounded by homes. Arnold Creek has riparian corridors wider than  in good condition, while Falling Creek's riparian zones, surrounded by homes, are in poor condition. Damaged zones from which native vegetation has been removed lead to erosion, stream bank failure, sedimentation, lack of shading, and higher stream temperatures.
Tryon Creek is among the few streams in the Portland metropolitan area with a run of  Steelhead Trout,  and Coho Salmon have been recorded spawning in the creek. Surveys by the Oregon Department of Fish and Wildlife in 2002 found Coho, Chinook Salmon, Steelhead, and Cutthroat Trout in different parts of the creek at different times of the year. None was present in large number. Cutthroat Trout had the biggest population, estimated at 53 individual fish during the spring of 2002. Water striders, invertebrates that can walk on water, are common in the pools of Tryon Creek. More than 60 species of birds, including Cooper's Hawks, Great Blue Herons, kingfishers, towhees, waxwings, and wrens frequent the area. Some of the resident mammals are bats, coyotes, moles, rabbits, skunks, and squirrels, while frogs, salamanders, snakes, and turtles also do well in the watershed.

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<section id="43083" fatherid="0" title="Parks" lv="" priority="7" level="1">
The state park includes a  bicycle path that runs along Terwilliger Boulevard on the east edge of the park as part of the Portland metropolitan area's system of greenway trails known as the 40 Mile Loop. Equestrians can ride through the woods on horse trails totaling about . Hikers can use the bike path, horse trails, and about  of hiking trails. A paved loop trail of about , furnished with drinking fountains and interpretive signs, can accommodate wheelchairs. A park building called the Nature Center houses a gift shop, a large classroom, space for educational exhibits, and a play area for small children.
Tryon Creek, which flows through the middle of the state park, also runs through Marshall Park, a modified natural area of about  in a canyon in the hills northwest of Mt. Sylvania. It features hiking trails, a playground, picnic tables, a waterfall, and a stone bridge over the creek. Other parks in the watershed include West Portland Park, a natural area of about , and Maricara Park, a natural area of about . Metro plans to acquire additional land along the creek to add to the parks.

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<section id="43084" fatherid="0" title="See also" lv="" priority="-8" level="1">
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<section id="43085" fatherid="0" title="References" lv="" priority="-9" level="1">
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<section id="43086" fatherid="0" title="Works cited" lv="" priority="-10" level="1">
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<section id="43087" fatherid="0" title="External links" lv="" priority="-11" level="1">
Category:Geography of Portland, Oregon
Category:Tributaries of the Willamette River
Category:Culverts

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