The Truttman Sink has a documented history of higher recession rates from wave activity in comparison to headlands to the north and south.
The original highway alignment between Kane Road and the north end of Big Lagoon and McDonald Creek was built on extremely unconsolidated and unstable uplifted marine sediments.
They brought with them livestock that would occasionally overgraze the natural meadows, which led to the burning of thick vegetation off the more gentle, rolling terrain to increase pastureland.
[4] Fine-grained materials make areas with mélange susceptible to erosion once saturated with water, which is important for the Truttman Sink due to the contact with the ocean and high amounts of precipitation.
[5] The clay component of the matrix is what causes most of the slope failures due to the absorption of large amounts of water combined with increased weight.
The area also consists of Sitka spruce (Picea sitchensis), twinberry honeysuckle (Lonicera involucrata), red alder (Alnus rubra), and skunk cabbage (Lysichiton americanus).