Hylebos Wetlands and Peat Sinkhole - Federal Way, Washington
Posted by: 
Hikenutty
N 47° 17.253 W 122° 19.569
10T E 550954 N 5237339
This sinkhole in a peatbog was formed due to contact with the oxygen in the water. It is 20 feet deep and is home to the native red-legged frog and an endangered variety of sedge.
Waymark Code: WM1CQ6
Location: Washington, United States
Date Posted: 04/06/2007
Views: 60
This sinkhole has been named the Hylebos(High-luh-bohs) Deep Sinks and it began its formation soon after the last glaciation of this area. When the ice retreated some 10,000 to 15,000 years ago it left a large lake that gradually filled with sediment and plant material. At some point it became dry enough to support forest growth.
Peat forms in low oxygen conditions. The plant matter is unable to fully decompose, due to lack of oxygen and the layers build up. This particular bog is 30 feet thick and it is one of few of the old type of peatbogs left. Most were mined for their peat years ago. The sinkhole formed due to the oxygen in the water of an underground aquifer. This oxygen allowed the plant matter in this spot to decompose fully and the result is this 20' deep hole.
This sinkhole is located in West Hylebos Park, which in turn is part of the Hylebos Watershed. The city owned park features a boardwalk trail meandering through the wetlands. There are interpretive signs along the trail, along with many benches and in one section, a bird blind. The area is home to several pileated woodpeckers and a host of other flora and fauna. Be sure to click on the gallery, because I we uploaded pictures of a rabbit and also some great fungi and flowers that we took while hiking to the sinkhole. There is a wonderful multi-cache called "Hylebos Wetland" in this park so be sure to check that out too.
The park entrance trail is located off of 348th St. next to the site of 2 historic cabins. There is parking at the cabins at N47 18.077 W122 21.782.
Follow the trail that winds around the right, smaller cabin. This trail will wind around until you reach the trail register kiosk at N47 17.271 W122 19.713. From here follow the trail next to the kiosk and take a left at the first junction. Continue following the boardwalk and you will reach the sinkhole coordinates.
Parking Coordinates: N 47° 18.077 W 122° 21.782
Public Transport available: yes
Waymark is confirmed to be publicly accessible: Not Listed
Access fee (In local currency): Not Listed
Requires a high clearance vehicle to visit.: Not Listed
Requires 4x4 vehicle to visit.: Not Listed
Website reference: Not listed
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Visit Instructions:
No specific requirements, just have fun visiting the waymark.