RED DEER, Alta. -- Thieves who stole an oilsands dump truck the size of a small house and then rampaged through several baseball diamonds have left the manager of the facility with a monster truck-sized headache.

Police said the incident happened late Friday night.

The joyriders drove the massive vehicle, which weighs about 161 tonnes, off a flatbed trailer, which had been parked near the baseball diamonds in northwest Red Deer.

RCMP said a semi hauling the big truck pulled into a parking lot by the ball diamonds just before 10 p.m. and unhitched the trailer.

The flatbed was left in the parking lot for approximately 45 minutes before thieves climbed into the dump truck and drove it off the trailer, causing extensive damage to both.

After badly damaging the trailer, the thieves then crashed through about 120 metres of chain link fencing, dragging it onto one of the diamonds, said Roger McKay, the technical director of the Central Alberta Slo-Pitch Association which operates the fields.

Leaking a trail of black hydraulic fluid, the dump truck driver then did loops through several of the four adjoining ball diamonds, crunching six of the eight metal and wood dugouts at the facility, McKay said Monday.

"(The driver) took out two dugouts, turned through the infield and took out two more dugouts, turned again through the infield and took out two more dugouts and that's when it came to a halt."

McKay thinks the thieves could no longer steer the giant vehicle when the hydraulic fluid ran out so they abandoned it on the infield of one of the diamonds and made a getaway. A large pool of the gooey fluid leaked onto the infield where the vandals had stopped the vehicle.

The truck was on its way back to the oilsands in Fort McMurray, Alta., after being serviced at a local machine shop, McKay said. He said he's heard that the keys were left in the ignition.

While earlier reports pegged the damage to the ball diamonds, the monster truck and the flatbed trailer at approximately $1 million, RCMP said Monday a dollar value hadn't yet been determined.

"It's senseless destruction. I don't understand why somebody would want to do that," McKay said.

"It doesn't do much for your thoughts of people and their social conscience, or lack of."

The city's environmental services division is helping to clean up the spilled fluid. The contaminated soil and shale from the diamonds will have to be removed and replaced with clean material, McKay said.

"I was told this morning by someone who knows that a very heavy vehicle like that can kill the grass. If you drive a vehicle that heavy over dormant grass, it quite often will not come back."

The association didn't carry any insurance, because premiums were too expensive. But McKay said service clubs and business are offering to help them repair the damage to the facility, which he said could cost up to $60,000.

Scott Wakefield, general manager of the Finning Canada machine shop where the truck was serviced, said a transport company picked up the vehicle Friday afternoon.

He said they loaded it onto a trailer, drove it down the street and parked it near the baseball diamond, but wasn't sure why they did that.

When he heard about the incident from one of his managers the next day, he went over to the ball diamond to survey the damage.

"That's the first time I've ever seen anything like that happen. It's surprising, for sure," said Wakefield.

"Why somebody elected to take it off a transport trailer, which damaged the engine as they were pulling it off, and drive it around -- you got me," he said.

An official with Sparky's Trucking, an Edmonton-based transport company, wouldn't comment on the incident, but said they're working with their insurance company on it.