GLENWOOD CANYON, Colo. -- A major rockslide left two large holes on Interstate 70 in Glenwood Canyon and it may be days before the highway is reopened.

Gov. Bill Ritter has declared a disaster emergency and issued an executive order Monday afternoon that allows the state to seek federal funding from the Federal Highway Administration to help pay for repairs.

"The largest boulders are estimated to be the size of a semi," said Stacey Stegman, a CDOT spokeswoman.

At least one hole in the westbound lanes is 10 feet by 20 feet. The slide occurred at mile marker 125, just west of the Hanging Lake Tunnel.

"It is a beautiful valley," said Michael Thompson, who was trying to get home. "But this is what happens when you live around the rocks."

Boulders were blocking westbound and eastbound lanes. Stegman said the boulders blocking the roadway are so big, they will have to blow them apart to move them.

The largest boulder was estimated to weigh approximately 66 tons, or 132,000 pounds.

The highway is closed for a 17-mile stretch through the scenic canyon.

CDOT geologists were on site Monday afternoon and were in the process of assessing a rock that appeared to be unstable, said Mindy Crane, a CDOT spokeswoman. The assessment requires a two-hour hike up the mountain, inspection and a two-hour hike back down.

If the rock is determined to be unstable, CDOT will not reopen any lanes of I-70 until rockfall mitigation can be conducted.

"[The geologist] said there are fractures around the rock," said Stegman. "It doesn’t look like it’s being held tightly in place. They can blast it from the hillside. They can use sort of an airbag type system. They pump air into it and it pushes the rock down.”

Because the assessment will take several hours to complete, and it's unsafe to work at night, mitigation work will not take place until Tuesday.

In the meantime, crews continue to blast the large boulders into smaller pieces for removal, Crane said. So far, crews have blasted three rocks and have several more to blast apart.

Alternate routes for traffic are from westbound I-70: exit at US 40/Empire to State Highway 13 and back to I-70; exit in Silverthorne and take State Highway 9 to US 40 and State Highway 13; exit at Wolcott/State Highway 131 to US 40 and State Highway 13. From eastbound I-70: exit at Rifle/State Highway 13 to US 40 and back to I-70. Travelers may also wish to use U.S. highways 160 and 285 if traveling to destinations south. US 50 to the south is open over Monarch Pass, but chains are required for all commercial vehicles.

The closest alternate interstate route is I-80 through Wyoming.

"Every mile you drive this thing costs a fortune," said David Stelly, a truck driver from North Carolina fueling up off I-70. "Every time you get near a metropolitan district it is going to cost you time."

Stegman said that preliminary reports from people on the ground is that Monday's slide could be worse than a similar slide that happened on Thanksgiving Day in 2004. Damage repair for the slide totaled nearly $700,000. No one was hurt because the highway had previously been closed for an unrelated crash.

A Feb. 26, 1995 rock slide along I-70 in Glenwood Canyon killed three people -- Kathy Daily and her two children, Tanner and Shea, ages 11 and 6.

The Union Pacific Railroad said its tracks through the canyon weren't affected. The tracks carry freight trains and Amtrak's California Zephyr.

Monday editions of the Glenwood Springs Post Independent and the Aspen Times were delivered late because the slide struck between their towns and their printing plant in the town of Gypsum.