Two dramatic rockfalls that sent tons of sandstone tumbling down the Rims this week lent a sense of urgency to a project to stabilize the towering cliffs above Zimmerman Trail.
The first fall occurred between 2:30 and 3 a.m. on Monday, when several massive boulders rolled down a ravine just west of Zimmerman Trail, missing a house by about 150 feet.
Barely half a day later, about 1:15 p.m., a similar formation, weakened by the earlier collapse, came crashing down, and the whole thing was captured on the dashboard camera of a police officer sent there to keep trespassers away from the area.
By coincidence, several representatives of the company hired to help work on the Rims above Zimmerman Trail had just arrived on the scene and witnessed the second episode of falling rocks.
Jamie Addison, the project manager with GeoStabilization International, said he and his associates were picked up at the airport a little after 12:45 p.m. and drove straight down Highway 3 to Zimmerman Park atop the Rims.
They had just stepped out onto so-called Monkey Rock above Zimmerman Trail when they saw fragments of rock shooting out from the bottom of a cliff face just to the west of where they were standing. Soon the entire enormous slab peeled away and fell down the talus slope below the Rims.
Addison said he has seen a few smaller rockfalls in the course of his work, but nothing like this.
“It was awesome,” he said. “It was Mother Nature at her finest.”
The two incidents probably also hastened City Council approval of an emergency plan to have GeoStabilization deal with one dangerous rock formation on the cliffs above Sixth Avenue North before its crews leave town.
The council voted unanimously Monday night to authorize the Public Works Department to work out an emergency contract with GeoStabilization for the Sixth Avenue work.
The state had originally planned to have work done on the Rims above Zimmerman Trail this fall, but the project was pushed forward when rocks fell on March 25, damaging the roadway and taking out a long section of guardrail.
“We basically accelerated the entire project,” said Debi Meling, the city engineer with Public Works.
Meling said Terracon of Billings, the engineering firm that did all of the preliminary work on defining the scope of the project and finding possible solutions, got much done in a very short time. She also praised the Montana Department of Transportation, which “really pulled out all this stops on this.”
She said it was almost unheard of to get a project of this size from the drawing board to the work stage in just under six weeks.
The city received a federal earmark of $7.2 million to make improvements to Zimmerman Trail nine years ago, Meling said. Part of that money was always going to be spent on reducing the chances of rocks and boulders falling onto the roadway.
Last Thursday, the MDT awarded a $718,000 contract to GeoStabilization, based in Grand Junction, Colo., to deal with six problem areas above Zimmerman Trail. Meling said MDT awarded the contract because the city’s federal highway funds had to be funneled through the state agency.
Even before the rockfalls this week, the city asked Terracon to look at the Rims above Sixth Avenue and to recommend any possible mitigation work in that area.
Meling said that area has always been susceptible to falling rock — “You get a boulder there every now and then.”
After looking at the situation on Monday, GeoStabilization officials estimated it could cost as much as $500,000 for the work above Sixth Avenue. But the estimate was derived from a one-hour inspection tour, Meling said, and she expects the price to come down.
Public Works Director Dave Mumford also told the council that one of the problem areas could be dealt with by city workers, who would take off some loose rock and use netting and other devices to prevent rockfalls.
Meling said GeoStabilization would probably be used to take down a large, freestanding formation on the Rims above North 10th Street. The rock looks almost like a statue because of how it sits alone and stands out so prominently.
For now, Meling said, no one knows exactly where the money will come from to pay for the work above Sixth. The council simply gave the department the OK to have GeoStabilization do the work.
Meling said it’s always difficult to predict when anything will happen on the unstable Rims ringing the city. The formation that is going to be taken down from above Sixth Avenue looks dangerous, she said, but who knows?
“That’s another one that could be here for another 50 years,” she said. “I wish I knew.”
Still, if anyone has earned the right to make such predictions, it’s probably Meling. She told Last Best News before noon on Monday that another giant slab, in the same area and probably bigger than what fell Monday morning, was highly unstable, and could well fall before the end of the day. A couple of hours later, it did.
Scott Kinne, who lives at 3439 Timberline Drive just west of Zimmerman Trail, was awakened between 2:30 and 3 a.m. Monday by what he described as a “dragging, rumbling sound.”
He went back to sleep and then heard a similar noise half an hour later. He thought it was high winds, which are not uncommon there, but when he got up and looked out through sliding glass doors to his backyard, “there was not a leaf moving.”
What he did see, in the light of his neighbor’s motion-activated outdoor lights, were huge clouds of fine dust. He went out with a flashlight and could see that there had been a rockfall, so he and his wife loaded up their dog and cat and headed for the Wal-Mart parking lot.
When the second episode occurred, Kinne had just arrived back home and his wife, Annette Stone, had just run out of the house when she heard the familiar rumbling up above. This time their house was damaged, but only slightly when a relatively small boulder put a divot in the back wall of the home.
The ravine next to their house was full of freshly fallen rock later Monday, including several immense boulders, many smaller chunks of stone and innumerable pieces of sandstone shrapnel scattered over the hillside.
Among the debris was one large gash in the ground, maybe 3 feet deep and 15 feet long, where one boulder went skipping before coming to rest.
Meling said the GeoStabilization International crews are expecting to start work in the next day or two and to be done by mid-June. One of their first tasks will be to haul in dirt and create a berm along Zimmerman Trail, to stop the movement of any rocks dislodged during their work and to protect the roadway.
With predictions that the spring will continue cool and wet, there could be more acts of God, as insurers call them, while the engineering project is going forward.
“This will be an interesting month,” Meling said.