During a family trip to Yosemite when he was a kid, Greg Stock remembers spotting a huge chunk of rock sheer off the 3,000-foot vertical cliff face of El Capitan and crash among the pine trees at the base of the valley.
“I wouldn’t say that moment shaped my future career exactly — I nearly forgot about the incident until I moved back to Yosemite as an adult,” Stock says. “But it did leave a big impression on me when I was a child.”
Nearly four decades later, Stock, the park’s first staff geologist, spends his days surveying Yosemite’s remote corners, studying its famous granite features and trying to predict where and when the next rock fall may occur. Last September, a massive rock fall killed a British climber at the base of El Capitan, the first fatality from a rock fall within the park since 1999. “We don’t know what the trigger was for that incident,” Stock says.