Douglas Hollow begins in a valley between Douglas Hill and Oak Ridge in North Branch Township. The stream passes through a small unnamed pond and flows south for several tenths of a mile before turning south-southeast for several tenths of a mile. It then turns south and crosses Pennsylvania Route 87 before reaching its confluence with North Branch Mehoopany Creek. Douglas Hollow joins North Branch Mehoopany Creek upstream of its mouth.
Hydrology
Douglas Hollow is not designated as an impaired waterbody. At a site upstream of its mouth, Douglas Hollow was observed in 2001 to have a pH of 7.2 and an alkalinity concentration of. The water hardness was and the specific conductance was 136 umhos. In a measurement in August 2001, when the air temperature nearby was, the water temperature in the stream's lower reaches was.
Geography and geology
The elevation near the mouth of Douglas Hollow is above sea level. The elevation near the stream's source is above sea level. Douglas Hollow is a high-gradient stream that flows in a generally southerly direction. The stream is wide and in an August 2001 study was found to be dry or nearly dry in its lower reaches, with the exception of some small, disconnected pools.
Watershed
The watershed of Douglas Hollow has an area of. The stream is entirely within the United States Geological Survey quadrangle of Jenningsville. It joins North Branch Mehoopany Creek near Lovelton. Douglas Hollow flows through a mix of forested and agricultural lands. The non-forested land is mostly in the middle and upper reaches of the watershed. A total of 55 percent of the stream's length is within of a road, while all of it is within of one. The population density of the stream's watershed was 3 people per square kilometer in 2000, putting it in a multi-way tie for the least densely populated sub-watershed of North Branch Mehoopany Creek.
History
The valley of Douglas Hollow was entered into the Geographic Names Information System on August 2, 1979. Its identifier in the Geographic NamesInformation System is 1173421. The stream has no official name and instead takes its name from the valley through which it flows. It is also known as Douglas Hollow Brook. Pennsylvania Fish and Boat Commission biologists performed a fish sampling and other studies on the streams in the North Branch Mehoopany Creek watershed, including one site on Douglas Hollow, in 2001. The stream was added to the Pennsylvania Fish and Boat Commission's list of wild trout streams in 2013.
Biology
Wild trout naturally reproduce in Douglas Hollow from its headwaters downstream to its mouth. However, in 2001, these wild brook trout populations were noted to be sparse. In a 2001 study, two wild brook trout with lengths ranging from were observed in the stream's lower reaches. The low trout populations were primarily due to difficulty for fish to physically access the stream. In addition to brook trout, three other fish species were observed in the lower reaches of Douglas Hollow: blacknose dace, creek chub, and sculpins. Douglas Hollow is classified as a Coldwater Fishery.
