The Brief Authorities say a third-grader brought a loaded 9mm handgun to a San Tan Valley school. An investigation is underway after authorities say a child brought a loaded gun to an elementary school in San Tan Valley. What we know:The incident happened on Sept. 22 at Copper Basin K-8, which is located near Copper Mine Road and Hunt Highway. What they're saying:The Florence Unified School District says the weapon was secured by school staff before deputies arrived. "Florence Unified School District commends the principal and Copper Basin Elementary staff for their professionalism and composure in addressing this serious situation.