Big Flat Road is a hiking, biking, and horse trail in Del Norte County, California. It is within Smith River National Recreation Area. It is 2.9 miles long and begins at 3,875 feet altitude. Traveling the entire trail is 5.8 miles with a total elevation gain of 1,057 feet. The Apex Mine (elevation 3,983 feet) and Thursday Evening Mine (elevation 4,006 feet) quarries can be seen along the trail.