The water in this hole is about 20 feet deep. Years ago there were two separate holes but over the two merged. The holes were most likely formed by decomposition of the peat soils, hastened by contact with oxygen in the water. Holes such as this are common in older bog wetlands such as the West Hylebos State Park wetlands.

The peat soils of this bog formed some 10,000 to 15,000 years ago in a depression left after the last glaciation. The depression originally held a lake that gradually filled with sediment and plant material until it became dry enough to support forest growth. In places the peat (organic plant deposits) is 30-feet thick.  Because peat forms in relatively low oxygen conditions the plant materials are only partly decomposed.   A core sample of this soil would show fragments from plants that died thousands of years ago. Due to urbanization and peat mining, however, very few examples of this type of wetland remain in the Puget Sound Region.

The water level in the hole is probably fed by a shallow aquifer (groundwater) from the Panther Lake area. A deeper aquifer called the Redondo-Milton Channel lies underneath this area, extending from the Redondo area southward toward Milton. Several wells in the Redondo-Milton Channel are the main source of drinking water for Federal Way.

The endangered red-legged frog (Rana aurora) favors the cool water of the Deep Sinks during warmer months and can often be seen here from spring through fall.