In the New York Botanical Garden, the river flows within a fault line and between cliffs of blended Manhattan Schist and Fordham Gneiss—rocks that have been metamorphosed, or changed, by the tectonic forces that shaped the region. The waterfall in the Garden is the remains of a dam that powered several mills that manufactured snuff between 1792 and 1870. The current Stone Mill was built in 1842.

Be cautious upon entering the gorge. Note the signs warning of a dam (waterfall) ahead and directing paddlers to a portage on the east (left) bank. This portage requires a 0.1 mile walk with your paddling vessel up and down a hill. Follow signs which takes you over the Stone Mill bridge and back down south under the bridge to access waterfront portage once more. Wheels and cartages are recommended.