The catastrophic event in 1906 that greatly affected urban development in California was the San Francisco earthquake. Occurring on April 18, the quake and the resulting fires devastated the city, destroying an estimated 80% of it and leaving over 200,000 people homeless. The disaster highlighted the vulnerability of urban infrastructure and led to significant changes in building codes and city planning in California. The reconstruction of San Francisco became an opportunity to modernize the city, resulting in a more resilient urban landscape. This event also prompted greater awareness of seismic risks in California, influencing future engineering and disaster preparedness efforts.