While Copper and Brownstone Falls are the main attraction, Red Granite Falls is a great side hike at Copper Falls State Park.
Starting at the parking lot for Loon Lake, follow the signs for Red Granite Falls across a grassed yard and into the woods. The trail is a wide, well-maintained gravel trail that creates a figure-eight loop as it crosses itself twice.
Halfway along the trail (regardless of which loop direction you take) you end up along the Bad River, and can hear the roar of Red Granite Falls. Several small trails down the hill to the west lead to various overlooks of the falls and the small ravine that it carves.
This is also a great hike if you want to take your dog for a long hike to a waterfall as Copper Falls State Park doesn't allow dogs on any other trail in the park.