When construction workers Thomas Williams, Ken Piercy and Brian Wood started digging on the corner of Sol-Wil-Le-No Avenue and the Esplanade, they expected to find concrete, dirt and maybe a few old bottles.

What they found instead was memory itself, sealed in a copper box.

A time capsule, lost and forgotten for 89 years, lay in waiting underneath a monument dedicated to John and Annie Bidwell, Chico’s founders.

Williams, Piercy and Wood were the only workers at Bidwell Mansion that day and were moving the monument to make way for an improved sidewalk.

“The day that we took it off we were on the crane,” Wood said. “We were standing there and we popped it up and we saw the black box.”

Wood and his co-workers immediately knew the box was something special. They called city parks officials to come examine the time-lost capsule, but couldn’t help doing some of their own investigating.

“I picked it up — it was pretty light,” he admitted a little guiltily. “I shook it a little bit and flipped it over. I wasn’t the only one who did it.”

The box itself was small and light. Dust and smoke rose from its lid as state parks official Shawnee Rose sawed it open at 10 a.m. on Saturday. More than 1,000 onlookers from Chico and neighboring cities gathered to get a look at the capsule.

“Eighty-nine years ago in 1925, important historical events were taking place,” Eduardo Guaracha, Northern Butte State Park superintendent, said in his speech before the box’s opening. “Calvin Coolidge was inaugurated as a United States president, and for the first time, people across America could hear the ceremony over the radio.”

State parks officials estimated the time capsule’s age based on the monument’s.

Guaracha said they combed through nearly century-old newspapers until they found a story documenting a festival dedicated to John and Annie Bidwell.

“On Oct. 16, 1925, thousands of residents of Chico, similar to today, gathered in front of the Bidwell Mansion to commemorate a monument to remember and honor the legacy of one of California’s greatest pioneers,” he said. “On that day, 89 years ago, a time capsule was sealed and placed at the base of the monument erected to the Bidwells.”

Guaracha and the other parks officials were amazed to see that there were no records of the time capsule’s existence. After its burial, the copper box disappeared from sight and memory altogether.

“If not for the unexpected findings of the city sidewalk revalue project, the box may have remained undisturbed for another 89 years, or hundreds of years,” he said.

The crowd’s anxious excitement could barely be heard over the saw’s buzz, but as smoke and dust cleared away, the crowd went silent. The crowbar came out, and the lid was pried off.

Flutters of nervous laughter and looks of bemusement crept onto the faces of parks officials and the crowd alike. From a distance, the capsule looked to be filled with straw, maybe a couple blocks of wood.

Sighs of relief replaced laughter as Kirk Coon, supervising ranger, announced that the box was actually full of what appeared to be paper scrolls wrapped up in hay.

The crowd shuffled after the time capsule as it was taken to the Bidwell Mansion Visitor’s Center to be put on display. Amongst the throng was Keith Earnest, a relative of the Bidwell family.

“Certainly it’s a connection to our family and to our heritage,” Earnest said.

His family had run wild with speculation over what could be inside the time capsule.

“We were hoping for objects,” he said. “Like maybe gold or commemorative coins or something like that. Or maybe Annie Bidwell’s missing diamond ring.”

John Bidwell found a three-carat diamond in the Feather River Canyon and had it made into an engagement ring for Annie, Earnest said. The ring disappeared after John and Annie’s deaths, and its whereabouts remain a mystery to this day.

“That would be amazing because no one knows what actually happened to the three-carat diamond,” said Earnest. “You know, John Bidwell was a very hard worker, but things like finding a three-carat diamond — that just doesn’t happen.”

The capsule’s contents are too delicate to be handled by just anyone, and will have to be examined by a professional, Guaracha said. If the parks department can’t find a local professional up to the task, the box will go to Sacramento to be examined.

As of now, the small, patinated box is on display in the Bidwell Mansion Visitor’s Center, open for the public to see. Its contents, however, remain a mystery yet to be revealed.

Zachary Phillips can be reached at [email protected] or @ZachSPhillips on Twitter.