Ralph DelPozo dug with a hand shovel for two days.

No luck.Then construction crews came with a backhoe and scooped an area 6 feet deep, 20 feet wide and 35 feet long.

Still nothing.

And what was all this searching for?

A time capsule, supposedly buried by eighth-graders on the grounds of Moon Mountain Elementary School in northwest Phoenix during the country's bicentennial in 1976. More than two decades later, says DelPozo, the school's facilities manager, no one is sure the time capsule even exists.

Moon Mountain officials aren't the only ones who end up with no time capsules in hand. Many capsules fail to age gracefully: Either the memory of their location fades or the capsule's documents and photographs deteriorate.

From Chandler to Glendale, schools, city halls, museums, shopping malls and churches have buried time capsules. The capsules are used to commemorate a special occasion such as the opening of a building or a celebration.

How will future generations know when it's time to open the capsules? In some cases, there's a 100-year wait.

Students grow up, politicians and bureaucrats leave and businesses come and go. Churches likely have the most continuity, but leaders may not have correctly recorded where the time capsule was buried.

In Moon Mountain's case, school officials, including DelPozo, were unaware that the time capsule even existed until Phoenix resident Robert Fenchak alerted them. Fenchak was one of the eighth-graders who made the time capsule as a class project.

"I thought I remembered where it was buried within about 10 feet," said Fenchak, who was surprised that the capsule wasn't there.

Principal Mary Lou Palmer said another former student also remembered the time capsule but wasn't sure where it was buried. She was unable to track down Fenchak's eighth-grade teacher who has retired and reportedly moved to Hawaii. Former principals and longtime teachers don't remember the time capsule.

In 1987, Chris-Town Mall officials tried to dig up a time capsule that was buried 25 years earlier at the mall's opening. They couldn't find it under the flagpole where it supposedly was.

That same year, the new principal of Glenn F. Burton Elementary School in Glendale accidentally found a time capsule while cleaning a closet.

As it turned out, he discovered the 18-inch piece of pipe just months before it was supposed to be opened. In 1972, the school's first principal had intended to bury it, but the school was under construction, so he stored it in a trophy case. New principals came and went, and the time capsule ended up in a closet.

Time capsules are sometimes mistaken for something else.

In San Diego, firefighters evacuated 500 students from a school in 1993 and tried to detonate what they thought was a pipe bomb. Instead, they got a blast from the past - the canister was a time capsule buried by students in the 1950s.