The Pioneer Cabin Tree, a sequoia, spent more than 100 years of its life standing tall in Calaveras Big Trees State Park in Arnold, California, as an all-natural tunnel. Hollowed out in the 1880s as a means to allow horses, hikers, and (for a time) cars to pass through, the tree was one of the most famous in the Golden State. But on Sunday, the 150-foot-tall Pioneer Cabin Tree collapsed in the midst of last weekend’s massive winter storms that dumped inches of rain and feet of snow across California and the rest of the West. A volunteer at the park, Jim Allday, told SF Gate that the tree crashed around 2 p.m. on Sunday afternoon and seemingly “shattered” on impact. And while the exact cause of the Pioneer Cabin Tree’s death isn’t certain, Jim's wife, Joan Allday, said that the tree had weakened significantly and was leaning excessively 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 weakening system, along with the strong storms and flooding, just proved to be too much. Sadly, the Pioneer Cabin Tree isn’t the only sequoia in Calaveras Big Trees State Park to fall after being hollowed out to accommodate a tunnel. In fact, the Pioneer Cabin Tree was modeled after the hollowed-out Wawona Tunnel Tree, which was killed by the process and then fell in a storm in the 1960s. As it turns out, the process of hollowing out a giant sequoia unsurprisingly cripples these ancient trees. As Travis M. Andrews wrote in the Washington Post, “These trees are made to burn, their protective bark healing itself over time,” Andrews writes. “Carving into a fire scar slows this progress.” Other than the Wawona Tunnel Tree, there have been several other natural structures that Mother Nature and human engineering have led to unfortunate downfalls. Here are six of them.