* Storm drops over three feet of snow in Black Hills region
* Even firetrucks are stuck in snow in South Dakota
* Power outages affect thousands (Adds details on stranded motorists and power outages)
By Kevin Murphy
Oct 4 (Reuters) - A rare and fierce October snowstorm rolled out over the central Rocky Mountains on Friday, stranding motorists, downing trees and forcing closures of hundreds of miles of Interstate 90 across parts of Wyoming and South Dakota, officials said.
The storm dropped more than three feet (90 cm) of snow in parts of the Black Hills region of western South Dakota, according to a Rapid City National Weather Service report.
An unknown number of motorists were stranded in Pennington County in South Dakota, Alexa White, spokeswoman for Rapid City-Penngton County Emergency Management, said.
Some called emergency services to say they were out of gas and feared they might not stay warm through the night, and rescuers in snowcats were trying to reach them, she said.
Four-wheel-drive vehicles and even rescuers in firetrucks were stuck in the snow, White said. Fire stations have opened as emergency shelters.
Thousands of people in Pennington County homes were without power, White said.
South Dakota Governor Dennis Daugaard ordered state offices closed in the Black Hills and six counties in the southwestern part of the state and said further closures are possible.
About 380 miles of Interstate 90 were closed from western South Dakota to northeastern Wyoming, according to transportation departments in both states.
"It's not normal this time of year, but it is not unheard of," Cory Martin, meteorologist for the National Weather Service in North Platte, Nebraska, said. "But this amount of snow for an October storm is on the higher end."
The National Weather Service, which is running on a reduced staff because of the federal government shutdown, issued blizzard and severe winter storm warnings across the northern part of the Great Plains through Saturday morning. (Additional reporting by Kayla Gahagan in Rapid City, Heide Brandes in Oklahoma City and Lisa Maria Garza in Dallas; Editing by Louise Ireland and Alex Dobuzinskis)