Previously a mystery, era in which the Ashidani Formation was formed in the Hida Gaien Belt at Kuzuryu is determined. The detrital zircon SHRIMP U–Pb age of Ashidani Formation sandstone is found to be within the range of 280 and 220 Ma. The most recent generation noted in samples collected is 224.2 ± 5.4 Ma (between the Carnian and Norian stages of the late Triassic Period). The metamorphic muscovite K–Ar age of sandstone schist is 182.6 ± 3.9 Ma (between the Pliensbachian and Toarcian stages of the Early Jurassic Age). There are no previous reports on metamorphic age values of 180 Ma in the Hida Gaien Belt. According to these dating results, geological development of the Ashidani Formation was limited to between the latter part of the late Triassic period and the start of the early Jurassic period, and can be compared to the Chizu metamorphic belt in the Chugoku region. Geological development of the Ashidani Formation is limited to the start of the early Jurassic period. Ashidani Formation Rocks were deposited in the forearc region of the eastern margin of the China craton at the beginning of the early Jurassic period. They then underwent high-pressure metamorphism alongside protoliths of the Chizu metamorphic belt in the middle part of the early Jurassic period due to subduction of the oceanic plate.