Abstract: At 9:51 a.m. on July 22, 2020, an employee and their coworkers were training/learning to be firefighters at the Chiquito Canyon Training facility of the Los Angeles County Fire Department. At 1:16 p.m. on July 22, 2020, DOSH was notified. Around 7:00 a.m., the employee and coworkers got ready for their hike, packing their packs and gear. They carried with them a 64 oz. canteen filled with water and two 16 oz. water bottles. Between 8:00 a.m. and 9:00 a.m., the employee, coworkers, and wildland cadre gathered together and commenced the hike. The hike was paced, with the wildland cadre stopping periodically to provide terrain instruction to the employee and coworkers (teaching them techniques to cut a line, choke flames, etc). The employee stated feeling well throughout the hike, at no point did he feel any signs or symptoms of heat illness. Then, the incident happened right before reaching the last incline of the hike, shortly after the entire group had rested. After resting for a few minutes, the employee and coworkers began the last stretch. A few yards out of the rest area, the employee began to feel cramps and stopped. The employee took out a packet of Drip Drop (an electrolytic powder), to mix with their water. The employee took off his gear pack, and was attended immediately by the cadre. The employee was taken to the ambulance that was onsite and transported to the hospital, where he was admitted and treated.