Assertion: progressive rock | /r/CapableOf | reach the peak of its popularity
Facets:
value: in the early 1970s
type: TEMPORAL
Source sentences:
text: Progressive rock (shortened to prog, or prog rock when differentiating from other “progressive…” genres) is an ambitious, eclectic, and often grandiose style of rock music which arose in the late 1960s, reached the peak of its popularity in the early 1970s, and continues as a musical form to this day.