From the club website:

When TPC Eagle Trace was built in 1983, it became just the second TPC course, and the first member-based club, in a network the PGA TOUR started developing around the United States (the first was TPC Sawgrass, home of the Players Championship). That’s why golfers will see spectator mounds around the course, including grandstand-type seating carved into the area surrounding the 18th green.