Fallow Hollow is a tributary of Coles Creek in Columbia County, Pennsylvania, in the United States.

[2] Fallow Hollow joins Coles Creek 2.54 miles (4.09 km) upstream of its mouth.

[8] The Columbia County Natural Areas Inventory of 2004 recommended that the riparian buffer around the wetlands in Fallow Hollow remain undisturbed.

[7] Fallow Hollow is listed as a "locally significant site" on the Columbia County Natural Areas Inventory.

[7] In the higher elevations of the watershed of Fallow Hollow, the forest canopy consists of trees such as red maple, sugar maple, red oak, white oak, yellow birch, serviceberry, Eastern hemlock, and big-tooth aspen.

The hollow's seepy woods contain trees such as white pine, yellow birch, and eastern hemlock, and pignut hickory.

Other plants in this part of the hollow include Japanese barberry, lowbush blueberry, partridge berry, red trillium, Indian cucumber, and witch hazel.