The stream rises out of a swamp between the Wyanokie Crest and Buck Mountain. It is characterized by a meandering path, broken up by several decent waterfalls including Otter Hole and the impressive Chikahoki Falls.
Looking at the area topography, there may be evidence of stream capture. Blue Mine Brook and a tributary of West Brook seem to be slowly eroding toward each other and may eventually meet with Posts Brook or one another. The result would be an act of stream piracy, wherein the runoff from one stream is captured from another, effectively cutting off the water supply from the unlucky stream. Without knowing more details, it's hard to say which is capturing which.
Downstream, the first major waterfall is Otter Hole. It is the namesake of Otterhole Rd, and "OH Parking" is the second most popular trailhead in Norvin Green State Forest. Several unnamed cascades are located downstream from Otter Hole. Most of these require bushwhacks. The stream levels out before it passes the yellow Wyanokie Crest trail, which is a complicated stream crossing during high water.
After receiving its most significant tributary off the slopes of Carris Hill, the stream begins to lose elevation again, passing a wider waterfall that's vivid and loud with increased flow. But the most striking cascade lies just ahead.
Named for after a Lenape word meaning "turkey lands", the 30-foot Chikahoki Falls is Posts Brook's greatest asset. Its flow rate is highly variable, from a barely-visible trickle to a roaring whitewater double cascade. It can serve as a indicator of drought or moisture surplus in the Wyanokie Region. The waterhole's shoreline similarly fluctuates between a smaller pool and inaccessibly flooded.
Below Chikahoki, the stream flattens out and flows towards the town of Wanaque, NJ. It passes by a spur that runs off into the Wanaque Reservoir through a gorge.
It briefly merges with Blue Mine Brook to form Lake Iosco. An eastern outlet continues as Posts Brook into Rainbow Lake, flowing beside part of Doty Rd. Finally, Posts Brook closely follows Ringwood Avenue as the South Twin Lake before it crosses under the street through a culvert. It merges into the Wanaque River approximately 6.75 miles from its source.
Though this waterway is short and partially protected from access by the NJDWSC, it contains a gorge with several cascades. It rises out of the Rockburn Springs of Long Swamp Mountain. Exiting out of the Long Swamp itself, it makes contact with West Brook Road just east of Otterhole Road's terminus. Not many cascades can be found here, but this area of the Brook can be accessed from Black Rock parking at Kiwanis Campground Road. It continues east past a tributary that receives water from the Kitchell Lake dam. Another tributary follows right behind, with water from the dammed Boy Scout Lake in Camp Wyanokie. From here, the West Brook reaches its gorge, containing several cascades of photographic interest.
After the gorge, the Brook enters Wanaque Reservoir watershed property that is strictly protected against trespassing by NJDWSC patrol and security cameras. West Brook continues past a farm after which it receives water from the Burnt Meadow Brook. It quickly empties into the Wanaque Reservoir thereafter.