The peaks look as though they were carved by something impatient. In a sense, they were. Jiujiufeng sits within the Toukeshan Formation, a Pleistocene-era geological unit composed primarily of gravelly rock — the compressed deposits of ancient rivers and alluvial fans that once covered this part of central Taiwan. The critical factor is permeability. Because the gravelly soil drains quickly and holds little cohesion against running water, rainfall attacks the slopes efficiently and continuously. Every storm removes a little more. Over Pleistocene timescales, this process cut the formation into the tight cluster of sharp-sided peaks visible today — each one a remnant of what the formation once was, separated from its neighbors by gullies cut by the same rainfall that is still at work. The result is a topography that looks almost deliberate: dozens of pointed summits arranged in dense proximity, their ridgelines serrated against the sky.

The 921 earthquake of September 1999, which struck just a few kilometers to the southwest along the Chelungpu Fault, left visible marks on Jiujiufeng. Landslides stripped vegetation from many of the slopes, leaving bare grey rock and gravel exposed across broad sections of the reserve. In the immediate aftermath, the peaks looked denuded and raw. Recovery has been gradual — not sudden revegetation but a slow reassertion of plant life on terrain that does not make things easy for roots. Despite the thin, permeable soils and the steep faces, Jiujiufeng sustains a notable variety of plant life, including the rare Reevesia formosana — a small flowering tree endemic to Taiwan and one of the conservation priorities that justified the reserve's protected status. The earthquake stripped the slopes; the plants came back.

A single hiking trail, 1.93 kilometers long, makes a loop through Jiujiufeng. Accessible from Caotun, on the Nantou side of the reserve, it threads between the peaks rather than over them — the terrain is too steep and fragile for summit routes. The trail offers close-up encounters with the formation's characteristic geology: the gravelly slopes, the gullied faces, the narrow ridges separating individual peaks. At sunset, the silhouette of Jiujiufeng becomes particularly striking — a jagged skyline against the orange and pink light over the Taichung basin to the northwest. The reserve spans multiple administrative areas, touching the cities of Caotun and Guoxing in Nantou County and Wufeng and Taiping in Taichung City. The shared jurisdiction reflects the range's position exactly on the county boundary, which in this part of central Taiwan also marks the transition from basin to foothills.

Jiujiufeng occupies the geological and geographic boundary between two worlds. To the west, the Taichung basin spreads flat and densely inhabited — farms, cities, highways. To the east, the Central Mountain Range begins its serious ascent toward Taiwan's highest peaks. Jiujiufeng is neither: it belongs to the zone of heavily folded and eroded foothills that marks the collision between the Philippine Sea Plate and the Eurasian Plate, still in slow, geological motion. The Dadu River flows along the southern edge of the reserve, one of the headwaters feeding the river system that drains central Taiwan westward to the Taiwan Strait. Standing on the loop trail and looking west at sunset, you are looking from active geology toward the settled human world — a useful reminder that the ground underfoot in central Taiwan is never entirely still.