Ikeda Area

In downtown Ikeda, you might notice some changes in elevation. One of the most noticeable is a 20–30 meter-high cliff between the Ueno and Machi-Sarada districts. The fault scarp was formed by the Ikeda Fault of the Median Tectonic Line, an active fault system and runs directly beneath the fault scarp from east to west. When the Ikeda Fault moved, the land on the northern side was pushed up by several tens of centi meters, and the fault scarp also shifted sideways by a few meters. These movements happened many times over a long period, gradually creating the fault scarp we see today.

Along National Route 32 (also known as Inohana Road), on the way from Shuzu of Ikeda Town toward Kagawa Prefecture, you can see outcrops of the Ikeda Fault—part of the active Median Tectonic Line, an active fault system. These outcrops are protected by transparent display boards. The southernmost board shows the actual surface of the fault. As you move north, the outcrops show less intense fault-related fracturing. On the southern side of the fault, you will find layers of conglomerate deposited in the Yoshinogawa River. Here, you can see fault-fracture zones of the Izumi Group.
*Please note: There is no sidewalk near the display boards, and approaching them is not allowed. For your safety, please view the outcrops from across the road.

The Median Tectonic Line (MTL) is a major fault that separates different types of geological formations. North of the MTL, the land is mostly made up of sandstone and mudstone, while the southern side is mainly crystalline schist. However, Shinyama—a low, gently sloping hill located on the southern side—is also made up of sandstone and mudstone. This is unusual, because it does not match the typical geology of the area. The reason is that landslides from the Sanuki Mountain Range, located to the northern side, once crossed over the MTL and deposited these materials of landslide blocks on the southern side. This is how the land of Shinyama Area was made.

Nishiyama Village is one of several settlements located in the middle of the Sanuki Mountain Range. The village sits on gentle slopes that were formed by past landslides.

It is believed that past landslides once blocked the Umajigawa River, located to the south. Today, the river is unusually narrow—one of the clues that suggest it was once dammed by landslides.

In the Nakanishi District of Ikeda Town, you can see layers of conglomerate made up of various shapes and sizes. These layers were formed by the Yoshinogawa River's flow, which made up the fluvial terrace.

Ikeda Castle, known as one of the Awa Nine Castles, was dismantled following the 1638 law that limited each province to just one castle. The remaining stone walls showcase traditional construction techniques from the 1600s. Interestingly, the stones used come from both sides of the Median Tectonic Line; crystalline schist from the south and sandstones from the south.

Hashikura Temple is located in the middle of the Sanuki Mountain Range. Along the temple’s approach stands at a very tall lantern. This lantern once served as a kind of “river lighthouse,” guiding boats traveling along the Yoshinogawa River at night, from downstream to upstream.

At the base of the Hesokko Ohashi Bridge, spring water flows up from underground—considered by some to be gifted from the movements of the Median Tectonic Line. Around the MTL, layers of crushed rock mixed with groundwater create sticky, clay-like barriers that naturally hold water back. The spring appears slightly away from these layers, where water finds a path to the surface. In the past, local people used this spring water for hot springs or onsen.

Kurozo Marshland is home to a variety of plants and animals adapted to marshland environments. Some rare species of plants and dragonflies can be found here. The marshland is shaped by several factors: 1) flat terrain and water flowing in from nearby mountains, 2) high elevation and cold temperatures, and 3) surrounding Japanese red pine (Pinus densiflora) forests, which lead to poor soil conditions and inhibit the growth of other tree species. These conditions help preserve the unique ecosystem of Kurozo Marshland.