Bull Creek is the largest Eel River tributary drainage basin preserved within Humboldt Redwoods State Park. The basin contains the world's largest remaining contiguous old-growth forest of coast redwoods. Bull Creek flows in a clockwise semi-circle around 3373-foot (1028-meter) Grasshopper Mountain to enter the South Fork Eel River approximately 1.5 miles (2.5 km) upstream of the South Fork confluence with the Eel River.