These lamprophyre dikes are a famous geological site where black lamprophyres are embedded in the cracks of white granite, creating a black and white stripe pattern.
One of the world's rarest dike formations, it was designated a National Natural Monument in 1942.
During low tide, you can even take a walk and see the lamprophyre dikes up close.
There are also areas around Higashikagawa City where one can find a range of impressive geological sites, which makes pleasure boat cruises to such sites a very popular activity.
* For cruises to geological sites, please contact the Higashikagawa City Tour Boat Association.