Please do NOT post your answers in your log. Send your answers at the same time as logging your find.
Marshall Park is an abandoned quarry formerly owned by F.C. and Addie Marshall and was donated by the Marshalls to the City of Portland. The Marshalls used to have a summer home near the Marshall Park Cascades and a pool near the creek. The scenic stone bridge is the only remaining infrastructure from their summer retreat. Tryon Creek is the stream flowing through Marshall Park and flows down Portland's West Hills (aka the Tualatin Mountains) for approximately 7 miles in a southeasterly direction and enters the Willamette River in Lake Oswego, Oregon. Marshall Park has excellent exposures of basalt visible at the cascades and along the cliff above the creek. The surrounding area contains the Columbia River Basalt Group that flowed from Eastern Oregon and Western Idaho followed by eruptions of Boring Volcanic Basalts from nearby Mt. Sylvania (a small shield volcano with an elevation of 978 ft). The basalts in this area are topped with a layer of Portland Hills Silt that blew in during the Pleistocene ice age. The silt is prone to sliding when wet. Excessive erosion is a concern in this area and is exacerbated by nearby development, specifically due to rapid water runoff on impervious surfaces such as driveways, buildings, and roads. The posted coordinates lead to the parking area for Marshall Park. Walk down the trail to the southeast to reach the waypoints. This earthcache takes you on an easy, short loop (approximately .5 mile) through a beautiful forested canyon. Please stay on the designated trails. There is no need to ever leave the trail to complete this earthcache.
1. Estimate the total height of the vertical cliff on the south side of Tryon Creek from the waypoint at the stone bridge.
2. Do the rocks in the stone bridge appear to contain the same rock type as seen in the cliff on the south side of Tryon Creek?
A picture of your favorite spot in the park is optional.
Please note that caching is only allowed during park hours, which are: 5 a.m. to 10 p.m.
https://www.portlandoregon.gov/parks/finder/index.cfm?action=ViewPark&PropertyID=252
Information for this earthcache was gathered from the following sources:
Habitat Management & Trail Plan, Marshall Park Natural Area, Portland Parks & Recreation
Roadside Geology of Oregon by Marli B. Miller
In Search of Ancient Oregon by Ellen Morris Bishop
The Boring Lava Field, USGS
The Geology of the West Hills, Forest Hiker
Geology of the Portland Area by Donald E. Trimble