Geology of the Jogasaki Coast 城ヶ崎海岸の地質
Official explanation
Cape Jogasaki is a small promontory that extends into the sea at the western end of the Izumi Mountains. Approximately 50 kilometers long and 10 kilometers wide, this mountain range runs from east to west and separates Osaka and Wakayama prefectures. The range declines in height as it makes its way westward, disappearing under the sea at this point. The islands of Jinoshima and Okinoshima, just offshore, are thought to have once been part of the range.
The geology of the Izumi Mountains took shape around 70 million years ago during the Upper Cretaceous epoch. It consists of sedimentary deposits of sandstone, mudstone, and conglomerate. The Japan Median Tectonic Line—Japan’s longest fault system at over 1,000 kilometers—follows the line of the Izumi Mountains.
Read the full explanation
At low tide, a jagged, washboard-like topography appears along the shore here. It consists of alternating layers of harder light-colored sandstone and softer, darker shale. Movement of the Earth’s crust has caused the rock formation to tilt, and the distinctive uneven topography is the result of the waves eroding the shale.
This rock formation is common along the Jogasaki Coast and around the Tomogashima island cluster. It contains fossils of clams, sea snails, sea urchins, crabs, and even sharks. Sole marks—small irregularities that are casts of a corresponding feature on the lower layer of sedimentary rock—are another distinctive geological feature. The rock or tide pools of the intertidal zone teem with sea life.
[ILLUSTRATION TITLES & CAPTIONS]
The origins of “washboard” topography
1. Layered sandstone and shale rock structure.
2. Movement of the earth’s crust tilts the rock.
3. Waves erode the softer shale layer.
Animals living in the tide pools
万潮時 High tide
潮間帯 Intertidal zone
干潮時 Low tide
潮下帯 Subtidal zone
潮だまり Tidal pool
石の下 Under rocks
カメノテ Japanese goose barnacle
岩の上 On the rocks
サザエ Turban shell
イソバナ Sea fan
イソギンチャク Sea anemone
ヤドカリ Hermit crab
イトマキヒトデ Blue bat star
ウニ Sea urchin
フジツボ Barnacle
出典: 地域観光資源の多言語解説文データベース（観光庁） — www.mlit.go.jp/tagengo-db. この英語解説文は観光庁の地域観光資源の多言語解説整備支援事業で作成しました。
Source: Japan Tourism Agency, Multilingual Explanation Database. This English text was produced by the Japan Tourism Agency's multilingual explanation project and is shown unedited. Opening hours and services may have changed since it was written.
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