Rondout Creek flows generally southerly down the slopes of Rocky Mountain into a narrow valley, receiving tributary Picket Brook on the left and three unnamed streams from the slopes of Peekamoose Mountain to the right. A mile or two from its source, it reaches some private lands and its first road, Peekamoose Road (Ulster County 42). It has dropped in its first two miles. It turns to the southwest to follow a wider valley, known informally as Peekamoose Gorge. Most of the land surrounding the creek is part of New York's Forest Preserve, "forever wild" and thus undeveloped. The rocky stream boasts several popular swimming holes, one of which is known as Blue Hole for the greenish tone of the deep water within. South of the small outlet stream from Peekamoose Lake, it is crossed and then followed by Peekamoose Road, which at first runs high above the creek but then close by it. Along here it receives several tributaries from the right — Buttermilk Falls Brook, with its eponymous waterfall near its mouth, High Falls Brook and Bear Hole Brook — most of them rising, like the Rondout itself, in the Slide Mountain Wilderness Area to the west. To the east is another Forest Preserve management unit, the Sundown Wild Forest. Some unnamed tributaries come from here. Because of the protected areas on both sides of the creek and the ease of public access, this area has become one of the Catskills' popular trout streams, and fly-fishermen can be seen here during the season. It crosses under Peekamoose Road, here also carrying the Long Path hiking trail, again just north of a popular camping area in the small Peekamoose Wild Forest, and then passes the hamlet of Sundown and widens slightly as a floodplain develops alongside. The land along the creek is now largely in private hands, and there is little public access to it as it crosses into Sullivan County. Reservoir to Napanoch After crossing under NY 55A, it widens into the reservoir just below Grahamsville and begins flowing more to the east-southeast. Routes 55 and 55A bracket the reservoir to the south and north respectively. One-third of the way along the reservoir's length, it crosses back into Ulster County. Now at an elevation of , the creek resumes at the site of the former hamlet of Lackawack, leaving the Catskill Park, now headed eastwards, in a rocky,