The North Coast region, which includes RNSP and the adjacent offshore area, is the most seismically active region in the United States. As a result of frequent earthquakes, rapid uplift rates have led to landslides, actively braiding and shifting rivers, and rapid coastal erosion.

The reason for all this activity is the geologic setting of the North Coast region. Three tectonic plates (thin pieces of the Earth's crust which float above the mantle) known as the North American, the Pacific, and the Gorda contact each other at the Mendocino triple junction. This junction lies offshore near Cape Mendocino, which is about 100 miles (160 km) southwest of RNSP.

Each of these plates slide against each other as they slowly move in opposing directions. Movement may be as much as two or three inches (5-6 cm) a year. Many times, this movement comes in the form of earthquakes, when built-up energy is released along fault lines that border the plates. Although the majority of these earthquakes are too small to be noticed, larger quakes are not uncommon.

In the 1990s, at least nine magnitude 6.0-plus earthquakes jolted the North Coast. This amount of large quakes was higher than in any other decade within the last century. Most of these quakes occurred offshore, resulting in one death and major financial losses. Because the Gorda plate is subducting beneath the North American plate, there is the possibility of a "great earthquake" occurring in the future.

Scientists believe that the two plates are partially locked together along a contact known as the Cascadia subduction zone. The frozen boundary between the two plates is called the megathrust. The megathrust is broken from time to time, but usually along small parts of the fault, resulting in small quakes. However, if a larger part is broken, a magnitude 8.0-plus quake is possible.

Studies have shown that the last great subduction zone earthquake took place 300 years ago. Intervals between such quakes are in the hundreds of years, so predicting the next one is difficult. But research suggests that eventually such a quake will occur. Disastrous effects are possible when visiting the redwood region; be prepared by following these precautions:

Falling objects cause the most deaths during earthquakes. If you are indoors, take cover under a sturdy desk, table, or other furniture. Hold onto your shelter and stay there until shaking stops. Stay clear of windows, fireplaces, wood stoves, and heavy furniture or appliances. Stay inside!

If outside when a quake hits, get into the open and away from trees, power lines, and buildings.

If you are driving when a quake hits, stay away from bridges, overpasses, and tunnels and avoid stopping under trees, light posts, power lines, or signs.

If you are in a mountainous area or near unstable slopes or cliffs, be alert for falling rock and other debris that could be loosened by the earthquake.

If you are at the beach or near the coast when a quake hits, tsunamis can arrive within minutes. Move to higher ground (at least 100 feet) immediately, preferably on foot.

Most of RNSP is underlain by rocks of the Franciscan asemblage, which is primarily composed of sandstones and mudstones. This rock unit is best seen along the coast from Enderts Beach to the mouth of Redwood Creek and in road cuts on the way to the Tall Trees Grove trailhead. Much of the Franciscan assemblage consists of rock that has been sheared and lifted from the ocean floor as a result of the plate action along the Cascadia subduction zone.

Tsunamis