The historic Pioneer Cabin Tree, a former "drive-through" giant sequoia in Calaveras Big Trees State Park in Calaveras County, was felled in California's weekend storms.

The tree was hollowed out in the 1880s to allow tourists to pass through it, and even allowed cars, but more recently has hosted only hikers. It was part of the "Big Trees Trail" at the state park.

Jim Allday of Arnold is a volunteer at the park who was working there Sunday. He said the tree went down about 2 p.m. and "shattered" on impact. He said people had been walking through the tree as recently as Sunday morning.

It's not clear why the tree fell, but probably had to do with the giant sequoia's shallow root system — the roots only go about two or four feet deep — and the fact that the trail around the tree was flooded due to rain.

"When I went out there (Sunday afternoon), the trail was literally a river, the trail is washed out," Allday said. "I could see the tree on the ground, it looked like it was laying in a pond or lake with a river running through it."

The tree had been among the most popular features of the state park since the late 1800s. The tunnel had graffiti dating to the 1800s, when visitors were encouraged to etch their names into the bark.

Related: Where you can still see walk-through and drive-through trees

Joan Allday, wife of Jim Allday and also a volunteer at the park, said the tree had been weakening and leaning severely to one side for several years.

"It was barely alive, there was one branch alive at the top," she said. "But it was very brittle and starting to lift."

A Facebook post by the Calaveras Big Trees Association on Sunday afternoon had more than 800 comments by Sunday evening, with many people sharing farewells and photos with the tree.

"Nature gave us this beautiful tree and Mother Nature took it down," said one Facebook user. "It was beautiful to see in person."