Yosemite National Park is alerting visitors to the potential dangers of "Summer Branch Drop" (SBD), a phenomenon where tree limbs can fall without warning, especially during hot summer weather. The warning follows a recent incident where a falling tree limb resulted in the death of a 29-year-old Google engineer.
Angela Lin was hiking with friends in the Tuolumne Grove in July 2025 when a limb from a giant sequoia tree struck her. Park officials stated that SBD occurs most frequently in black oaks during the summer, particularly on hot, calm afternoons when there is no wind. Unlike branch breaks caused by wind, which typically occur at the point where a branch attaches to the trunk, SBD breaks usually happen three to 12 feet along the length of the branch.
These falling limbs are often long and horizontal, sometimes extending beyond the tree's canopy. While some broken limbs show signs of decay or damage, many appear sound. The phenomenon is more common in older, less vigorous trees, and a tree that has dropped a limb once is susceptible to doing so again.
Park officials recommend several precautions for visitors. They advise against pitching tents or setting up picnics directly beneath the branches of large oak trees, especially on hot summer days. Visitors are also cautioned to avoid leaving infants or elderly individuals in such locations. If a loud cracking sound is heard overhead, people should move away from the tree immediately. Staying clear of trees that show signs of damage can also enhance safety and allows park staff to monitor and maintain tree health.
Authorities are requesting the public's assistance in reporting any fallen trees or branches to park rangers. It remains unclear how many previous incidents may have been attributed to SBD or if this was the cause of the limb that fatally struck Lin. The park has been contacted for further information.
