https://en.wikipedia.org/wiki/Hickory_Run_State_Park
那个 boulder field 是冰川的遗迹。你说的一点没错，和河床很象，地理学上有些解释，感兴趣可以自己狗一下。上面wiki里也有一些介绍。
The most notable feature of Hickory Run State Park is the huge boulder field located in the northeast corner of the park.[5] The boulder field can be reached by car on Boulder Field Road or by hiking the 3.5-mile (5.6 km) long Boulder Field Trail from the trailhead on SR 534. The field comprises about 720,000 square feet (67,000 m2) (16.5 acres (6.7 ha) or 0.026 square miles (0.067 km2)) in area (1,800 feet (550 m) east-west by 400 feet (120 m) north-south). The top of the boulder layer is virtually level with the approaching path.[4] This boulder field, known as the Hickory Run boulder field, is the largest of its kind in the Appalachian region. It consists of a very gently sloping expanse of boulders that occupies axis of a small valley with approximately 100-foot (30 m) of relief.[6] A coniferous forest with stony loam soils surrounds the Hickory Run boulder field.[7]
The boulders in the Hickory Run boulder field range from less than 3-foot (0.91 m) to more than 30-foot (9.1 m) in length. They consist of hard, gray-red, medium-grained sandstone and conglomeratic sandstone from the Catskill Formation which forms the adjacent ridgelines. The boulders at the northeast, upslope, end of the boulder field are generally more angular than those found downslope to the southwest. In the southwest part of the boulder field, boulders are typically subrounded and overlie a layer of small, polished clasts with a red weathering rind. To the southeast, there is a distinct group of boulders, which are less than 15-foot (4.6 m) long. They appear to be bedrock that is shattered in situ.[8][9]
