This trail is unmarked but easy to find as it traverses the coast line. There are several short trails that extend out to various viewpoints to observe the rugged coast, arches, or to watch the sunset.
The trail runs the length of the park from the north to the south (or vice versa) near the town of Mendocino. You can start the run from either end and there are several parking areas along the park road so you can check out different sections without running the entire trail. Many people use this trail for jogging and watching the sunset. This recent trip, I went early one morning around 6 a.m. for a peaceful and relaxing run. This is a trail I could walk or run every day.
As you run the coastal trail, take careful note of the rock formations just off the coastline. There are quite a few arches created by erosion from the waves beating the rocks. Some of the arches are easy to find while others are a little more difficult. Some have to be seen from a certain angle. Others are small but arches none the less. This is the most concentration of arches I've seen along the coast.
Whenever I am in Mendocino or Fort Bragg just north on the coast, I make time to visit Mendocino Headlands to watch the sunset. There are so many great location to watch from here. The rocks and cliffs protruding from the ocean make a great foreground as the sun sets on the horizon. This recent trip I found a pinnacle rock with the sun setting behind it. I thought it was very nice.