Hemlock Run begins on a mountain known as Roundtop in Davidson Township. It flows south-southwest for several tenths of a mile, receiving an unnamed tributary from the. It then turns southeast for a few tenths of a mile and receives an unnamed tributary from the before turning south-southwest and then south-southeast. The stream enters a deep valley and receives another unnamed tributary from the right. Over the next several tenths of a mile, it gradually turns south and reaches its confluence with West BranchFishing Creek. Hemlock Run joins West Branch Fishing Creek upstream of its mouth.
Tributaries
Hemlock Run has no named tributaries. However, it does have three unnamed tributaries. The first tributary is approximately long and joins Hemlock Run near its headwaters. The second tributary is approximately or long and the third tributary is approximately long.
Geography and geology
The elevation near the mouth of Hemlock Run is above sea level. The elevation of the stream's source is between above sea level. Hemlock Run has a bedrockgorge. Additionally, the stream has waterfalls along its length. There are several distinct arcuate ridges of till in the valley of the stream. The terminus of the glaciers during the late Wisconsinan period of glaciation was in the vicinity of Hemlock Run. There are two buried valleys near the stream, one on either side of its gorge and waterfall reach. One of the valleys follows Hemlock Run in a northerly direction. A small portion of the valley of Hemlock Run is on bedrock consisting ofsandstone and shale. The Wisconsinan Till Moraine occurs near the stream in its lower reaches, as does the Wisconsinan Bouldery Till. Both of these are glacial or resedimented glacial tills. The latter has boulders consisting of quartz, sandstone, and conglomerate on the surface. A resedimented glacial till known as the Wisconsinan Flow-Till also occurs near the stream in its lower reaches. The Wisconsinan Till occurs in the upper reaches of the watershed.
Watershed
The watershed of Hemlock Run has an area of. The stream is entirely within the United States Geological Survey quadrangle of Sonestown. It is in the eastern part of that quadrangle. The stream is situated on the northern side of North Mountain. There are wingwalls made of concrete in the vicinity of Hemlock Run. Upstream of these wingwalls, there are approximately of R-5 riprap along the stream's west bank. This riprap is in a layer that is thick. The Pennsylvania Game Commission has a permit to maintain the riprap and the streambed with the wingwalls.
