Protesters and bulldozers square off in the San Gabriel Mountains.

Protesters and bulldozers square off in the San Gabriel Mountains. (KTLA-TV)

ARCADIA, Calif. ( KTLA) -- A group of nature advocates retreated from their day-long protest Wednesday evening among a grove of century-old trees and were taken into custody.

The four protesters -- two men and two women -- were arrested and booked on suspicion of delaying a peace officer and trespassing, officials said.

Some protesters blocked a gate while the others hid among the trees in an effort to save 11 acres of oaks and sycamores from being torn down in the foothills above Arcadia.

Los Angeles County officials planned to clear 179 coast live oaks and about 100 sycamores to make way for sediment dredged from behind the Santa Anita Dam.

As bulldozers began pulling out the trees and dirt in the San Gabriel Mountains, some protesters climbed into the trees, according to a spokesman for the Department of Public Works. Sheriff's officials worked all day Wednesday to get the protesters out of the trees.

Around 8:20 p.m. Wednesday all protesters had willingly removed themselves from their posts throughout the area. Some protesters required a fork-lift to be taken down from the trees.

Earlier in the day, sheriff's deputies escorted actress and environmental activist Daryl Hannah from the site after she arrived to support the protesters.

"I came out just to support the community that is trying to put out some common sense and not cut down a paradise for a rubble pit," Hannah said.

By nightfall, officials said about 90-percent of the trees had been removed.

Protesters say they expressed concern about the plan weeks ago and even provided alternative sites for the sediment, but officials still pushed ahead with their plan.

"We understand the need to remove the sediment. We do not object to that in any way shape or form. What we're concerned about... is the fact that they're needlessly cutting down a mature grove of 119 oak trees. They needn't do that," David Czamanske of the Pasadena Sierra Club told KTLA.

Czamanske said the protesters who hid in the trees were not part of the Sierra Club.

All protesters were checked to be in good health.