After engineers spent most of Saturday unsuccessfully trying to break a large slab of sandstone from the Rimrocks, a separate chunk fell about three miles to the west above 38th Street West and Laredo Place.
Billings Fire Battalion Chief Boyd Vopel said a flat slab of sandstone leaning out from the Rims broke off and tumbled about 150 feet down a small ravine. The chunk of rock fell at about 7:15 p.m. above 38th Street West.
While no damage was reported, a number of rocks landed in a driveway of a home on War Bonnet Trail.
No evacuations were ordered, and nobody was home at the two houses on War Bonnet Trail that are closest to the rock fall.
Vopel said there doesn't appear to be any imminent danger and that the area will likely be assessed Monday.
Connie Unruh, who is in town visiting her son who lives on 38th Street West, said they were having dinner when the rock fell.
"It was like a crack of thunder," she said. "I looked up and dust was coming from everywhere up there."
The rock fall is about three miles west of a site above Granite Avenue near Cactus Drive where Accurate Concrete Cutting of Vancouver, Wash., spent Saturday trying to free a 340-ton slab of sandstone from the Rimrocks there.
Vopel said the rock fall on 38th Street West is not likely connected to the earlier work.
"I'm certainly not an expert," he said. "I would say there is absolutely no connection between Cactus and this."
Crews from Accurate Concrete Cutting, of Vancouver, Wash., worked from 10 a.m. to 6 p.m. using hydraulic jacks to push the top of the Granite Avenue slab nearly nine feet, but the rock hadn't broken free by Saturday evening. They plan to get back to work on that project at 8:30 a.m. Monday. That slab is part of a massive rock fall that destroyed a house at 1313 Granite Ave. last October.
Monday. For the weekend, crews secured the sandstone slab above Granite Avenue to the Rimrocks by wrapping cables around it and securing them to anchors drilled into the sandstone above.
Residents who had to leave their homes during Saturday's work were allowed to return home. They don't want to ask people to leave their homes on Easter Sunday, said Mike Whitaker, Parks Department director.
The slab is considerably more rooted into the Rims than engineers and Accurate Concrete Cutting, the company hired to remove the slab, had anticipated.
The workers have found that the rock's base is sitting in a kind of cradle, said Jon Thompson, parks superintendent for the Billings Parks and Recreation Department. So, even though hydraulic jacks keep pushing the rock out at the top, the bottom isn't moving.
"It's a 300-plus-ton rock," Thompson said. "When you're dealing with something that big, unforeseen things can happen."
The plan was to use the hydraulic jacks to slowly separate the huge rock from the Rimrocks, letting it fall to the ground below when it broke free.
Accurate Concrete Cutting had planned to bring the Granite Avenue slab down Saturday morning and then move five or six blocks to the east, above Shady Lane, to remove another dangerously hanging rock, estimated to weigh 300 tons. The city evacuated several houses on Granite Avenue, Cactus Drive and Smoky Lane for the first rock drop. One house on Shady Lane and three houses on Rimview Drive were going to be evacuated for the second rock effort.
There were problems throughout the day Saturday. The first issue that workers ran into was that the jack's piston, the steel shaft that does the pushing, was penetrating the relatively soft sandstone. Workers dealt with that problem by placing steel plates between the shaft and the rock.
Later, they found that the back of the jack was grinding away at the wall of the cliff, and that had to be braced with steel plates as well.
Vern Balkowitsch, a co-owner of Accurate Concrete Cutting, briefly considered using fire hoses to spray at the base of the rock to wear out the dirt in hopes of getting the rock to move, but decided against that.
Throughout the day, there were just a few times when small fragments of rock fell. The first and largest fall happened about 11:35 a.m., when a small boulder went tumbling down the slopes below the Rims, eliciting cheers from the spectators and city workers clustered in scattered groups outside a security zone marked off with police tape.
"It's a bit baffling why the darn thing hasn't come off," Thompson said.
Balkowitsch said he had never encountered this situation.
"This is one that nobody's ever seen before," he said, standing on the street below. "This is all new. It's one for the books."
When all was said and done, crews had widened the gap between the slab and the Rimrocks, which started at about two feet, to 8.5 to nine feet, Thompson said.
A crowd of people that showed up in the morning dwindled as the day went on, until late afternoon when just a few observers were left.
One of those observers, Vicki Dunaway, lives in a home on Granite Avenue almost directly beneath where the work was being done. She said shortly after 6 p.m. that she wasn't sure if she'd spend Saturday night in her home.
"I think they know what they're doing," Dunaway said. "But once that rock lets loose, who knows where it'll go."
Ryan Coles, an amateur photographer, had set up a camera on a tripod on top of the Rims a little west of Granite Avenue. He said he was busy Friday, so he was happy when he woke up and saw the bad weather that day.
"I didn't want to miss this," he said. "I was glad it was postponed to (Saturday)."
He was on the scene a little before 10, but by about 2 p.m., he'd had enough. He packed up his gear and left.
Thompson said crews will begin securing the area to start work again at 8:30 a.m. on Monday. On Sunday, they'll speak with people living in the area to go over the plans with them.
Once they realized the project would take longer than expected, Thompson and Balkowitsch scoured Billings for a larger, more powerful hydraulic jack. Nobody in town had one that suits their needs, so Balkowitsch ordered one flown in from his corporate headquarters. That jack will arrive Monday morning.
The project originally was scheduled to begin Friday morning, but snow, rain and high winds delayed the effort for a day.
The Washington company submitted a low bid of $189,000 for the two projects. The Billings City Council voted to pay only for the Granite Avenue job, which will cost $139,000. Two couples who live in the shadow of the rock above Shady Lane have arranged to pay Accurate Concrete $50,000 for their project.
The city got involved after a massive rock fall destroyed a house at 1313 Granite Ave. last October. The city called in engineers, who determined that the 340-ton slab still sitting on the ledge above the house posed a threat to area residents.
After the rock is dropped above Granite, Balkowitsch said his company will use heavy equipment to break up boulders behind and inside the ruined home, which is owned by Jon Lodge and Jane Deschner. Balkowitsch was already planning to be in town at least through next Wednesday to finish up that work.
The rock above Shady Lane became a danger in February 2010, when the bottom half of a pillar of rock broke loose and fell, leaving the top half hanging precariously above.
Deschner and Lodge spent the entire day watching as workers attempted to bring the slab down. They sat at a safe distance in lawn chairs on the grass of a neighbor's house, ready with a camera to record the event.
Both said they would come back on Monday to see the work finished.
"I do want to see what happened that changed my life," Deschner said.
Lodge, who was inside the couple's house when the boulders crashed into it last fall, said watching it this will will give him a different perspective on what happened.
"It's not often you get to see a reenactment of a disaster," he said.
Gazette reporters Ed Kemmick, Susan Olp and Zach Benoit contributed to this report.