Truttman Sink facts for kids

The Truttman Sink is a slow-moving earthflow (a type of landslide) located within the Humboldt Lagoons State Park in Humboldt County, California. It sits along the coast between the towns of Trinidad to the south and Orick to the north. This moving land mass drops soil and other materials into the northern part of Big Lagoon and the Pacific Ocean. This happens especially during heavy rain. The way the soil, rocks, and plants are arranged here shows it's a mix of an earthflow and a rotational slump (where land slides and rotates at the same time).

History of the Truttman Sink

The Truttman Sink area has always worn away faster from ocean waves compared to other nearby coastal areas. The name "Truttman Sink" was given by Caltrans (the California Department of Transportation). This is because the Truttman family once owned the land around these coastal cliffs.

The Old Highway 101

The first version of Highway 101 in this area was built on very loose and unstable ground. This ground was made of old ocean sediments that had been pushed up. For many years, Caltrans tried to fix the highway by paving over the parts that were eroding. But the land kept slipping. Finally, in 1971, Caltrans moved Highway 101 further inland to its current location. The old highway was then closed.

Early Settlers and Land Changes

In the 1800s, settlers and gold miners came to this area. They made big changes to the land. They brought farm animals that sometimes ate too much of the natural grass. This led to people burning off thick plants from the gently sloped areas to create more pastureland.

According to Richard Truttman, the headland (coastal cliff) was burned every other year in January. The original Sitka Spruce forest was either cut down or burned. This left the headland without plants for many years. This greatly affected how stable the slope was. The old highway was stable for a few years after it was built. But then it started to slip. At one point, the old highway surface was known to have dropped one meter (about three feet) overnight. This sudden drop is a key sign of the large land movement.

Geology of the Truttman Sink

The Truttman Sink is part of something called the Franciscan Assemblage (also known as the Franciscan Formation). This is a group of different rock types. It includes sedimentary rocks like sandstone and shale. It also has oceanic rocks like basalt and greenstone. Other rocks found here are chert, serpentinite, limestone, and several metamorphic rocks. These metamorphic rocks include blueschist, amphibolite, and eclogite. Franciscan rocks are found all along the California coast. They formed millions of years ago in a Mesozoic subduction zone. This is where one Earth plate slides under another.

What is Mélange?

The Franciscan Formation at Truttman Sink is mostly a type of rock mixture called "mélange". Mélange is a fine-grained mix of broken-down Franciscan rock types. Areas with mélange are easily eroded, especially when they get wet. This is important for the Truttman Sink because it's next to the ocean and gets a lot of rain.

Mélange zones usually have a lot of clay. This clay makes them break down easily from land movements and weathering (the breaking down of rocks). The clay is the main reason for most of the slope failures. This is because clay soaks up a lot of water, which makes it heavier and less stable. These slope failures cause large rocks and trees to move down the slope. They then end up on the beach and are washed into the ocean or lagoon.

When mélange weathers, it forms a sticky clay soil. People sometimes call this "blue goo" or "grey goo" because of its color. You can see this "goo" mostly at the bottom of the Truttman Sink hill. This is where there are fewer plants. But it can also be found higher up the slope.

Vegetation at Truttman Sink

The Truttman Sink area has many kinds of ferns. These include sword fern (Polystichum munitum), common polypody (Polypodium vulgare), coast polypody (Polypodium scouleri), and lady fern (Athyrium filix-femina). There are also several invasive plants like blackberry and annual grasses.

Other plants in the area include Sitka spruce (Picea sitchensis), twinberry honeysuckle (Lonicera involucrata), red alder (Alnus rubra), and skunk cabbage (Lysichiton americanus). Many more plant species grow on this coastal headland. But the Sitka spruce and skunk cabbage are most important for showing evidence of land movement.

Plants and Land Movement

The top of the slope has a mix of tanoak, Sitka spruce, and other plants. As you go down the slope, you see a change in plants. In the middle of the slope, you start to see skunk cabbage. This plant needs areas that are always wet. This wetness is the first sign that the land is moving, showing characteristics of an earthflow and rotational slide.

Further down this wet area, Sitka spruce trees start to lean backward. This happens because the rocks and soil beneath them are slowly moving towards the ocean. At the very bottom of the slope, the trees are leaning backward the most. This area also gets more wave action from the ocean. You can see hanging root systems exposed where the clay-rich mélange is.