CONCORD — Concrete hails down from the sky; chunks the size of bowling balls hit the ground with thud after thud. The whole 235-foot-tall Cowell stack wobbles as though it's slightly unsteady on its feet.

The jaws of a concrete pulverizer, hanging atop a 250-ton crane, chomp away at the icon of Concord's skyline, leaving a twisted mess of rebar emerging from the now-jagged top of the ever-shorter stack.

The jaws' 450 tons of pressure crush the concrete "like paper," said Mark Weinmann, the project manager for the Cowell Homeowners Association, which owns the stack.

The demolition started Tuesday morning, around 8 a.m. In a few weeks, little will be left of the stack which stood over the city for 73 years.

It is being demolished because it is unsafe — chunks of concrete were falling from the top, and it has been in danger of toppling over onto nearby houses.

Restoring it would have cost at least twice as much to repair it as the about $400,000 cost to tear it down, Weinmann said.

Demolition was going as planned Tuesday morning, he said.

"I think it's going to go really smoothly," he said. "We're all sad, but it's something we've got to do."

Once the stack is reduced to a height of 40 feet, contractors use a smaller lift to take down the remainder. Demolition should take less than two weeks, said Wayne Evans, vice president of Evans Brothers, Inc., the contractor in charge of the demolition.

The whole process should be done by the beginning of September, Weinmann said, including the construction of the commemorative pedestal which will sit inside the about two-foot-tall ring of the stack which will remain.

The stack, a remnant of the Cowell Portland Cement Co., was never actually a smokestack. Its job was to contain dust created in the process of making concrete and prevent the dust from settling on nearby crops.

The plant was shuttered in 1946 and its buildings razed in the 1970s, giving way to the houses that now stand only feet from the base of the stack.

Sandra and Warren Gertz, 21-year residents of the neighborhood, said they were sad to see it go.

"It was something you always made reference to," she said, sitting on a nearby bench watching the demolition.

She is glad that about two feet of the bottom of the stack will be left as a monument, she said.

Warren Gertz said he is torn about the demolition. He wishes the stack could have been saved, but said he and his neighbors would have had trouble paying the extra cost to preserve it.

His homeowners' association dues had already gone up to just to pay for the demolition, he said.

"My heart says one thing, but my head says another," he said.

Reach Paul Thissen at 925-943-8163 or pthissen@bayareanewsgroup.com.