Course
Tryon Creek begins slightly north of Interstate 5 (I-5) and Oregon Route 99W near Multnomah Village and flows southeast for 4.85 miles (7.81 km) 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 260 feet (79 m) then flows on the surface before entering another culvert, 160 feet (49 m) 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, 560 feet (170 m) long.
Tryon Creek receives Falling Creek from the right at 4.16 miles (6.69 km) from the mouth. Quail and Burlingame creeks enter from the right 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 right 2.68 miles (4.31 km) from the mouth. Almost immediately, the creek enters a culvert, about 150 feet (46 m) long, that passes under Southwest Boones Ferry Road.
Shortly thereafter, Tryon Creek enters the Tryon Creek State Natural Area. To the stream's right is the North Creek Trail. Soon the creek receives Fourth Avenue Creek from the left. At this point, the Fourth Avenue Trail runs parallel to the creek along the left bank. This trail soon merges with the Lewis and Clark Trail, which also runs parallel to the creek along the left 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 0.20 miles (0.32 km) before passing under the Beaver Bridge. In this stretch, the Middle Creek Trail parallels the stream along the right bank but crosses to the left bank at the bridge. Shortly thereafter, the creek passes under Obie's Bridge, which carries the Old Man Trail.
Park Creek enters from the right at RM 1.80 (RK 2.90). Slightly below the confluence, the creek passes under the Red Fox Bridge, which carries the Red Fox Trail. Thereafter, the creek runs roughly parallel to the South Creek Trail, which is on the right for about 0.40 miles (0.64 km). The creek receives Red Fox Creek from the right and Palatine Hill Creek from the left, then flows out of Portland and Multnomah County and into the city of Lake Oswego and Clackamas County. The stream then passes under the Iron Mountain Bridge, which carries the Iron Mountain Trail. Just below the bridge, Nettle Creek enters from the right at 1.06 miles (1.71 km) from the mouth, and shortly thereafter the creek passes a United States Geological Survey (USGS) stream gauge, which is on the right. The creek leaves the Tryon Creek State Natural Area just before entering a 200-foot (61 m) culvert under Oregon Route 43 at RM 0.24 (RK 0.39) and soon thereafter a set of Union Pacific Railroad tracks. Below this, Tryon Creek forms the boundary between the city of Lake Oswego and Briarwood, an unincorporated Clackamas County community, which is to the left. The Tryon Creek Wastewater Treatment Plant is on the right during this last stretch before the creek enters the Willamette River about 20 miles (32 km) upstream from its confluence with the Columbia River.
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