By Keith Coffman
DENVER (Reuters) - Three people were missing after a four-mile (6-km) long mudslide tore through a mountain community near the Grand Mesa National Forest in western Colorado on Sunday, authorities said.
Emergency crews were responding to the slide which occurred in Collbran, a town of 700 about 200 miles west of Denver, said Heather Benjamin, spokeswoman for the Mesa County Sheriff's Office.
The slide was estimated to be about two miles wide and about 250 feet deep in places and was described by deputies on the scene being very unstable, the sheriff's office said.
An entire ridge was believed to have been sliding for most of the day. A witness described hearing sound akin to a freight train, attributed to the slide, the office said.
"This slide is unbelievably big," said Lt. Phil Stratton in a statement, with a day of rain in the area a likely factor. Six straight days of rain have soaked large swaths of the Rocky Mountain state.
The National Weather Service in Boulder, Colorado issued an advisory this month warning that monsoon rains which caused flooding in the state last September could increase the possibility of landslides as the state's deep snowpack melts.
"The September 2013 rains likely destabilized hillsides and steep slopes, so increased landslides and rock slides will also be possible this spring, particularly with heavier or prolonged rainfall," the weather service said.
A mudslide two months ago buried much of a community in the Cascade foothills of Washington state, killing more than 40 people. County officials said on Thursday that a 42nd set of remains had been recovered from the rubble.
(Editing by Chris Michaud and Ron Popeski)