The Dongdae Mountains () are a small outlying range of the Taebaek Mountains. They run along the east coast of

South Korea South Korea, officially the Republic of Korea (ROK), is a country in East Asia. It constitutes the southern half of the Korea, Korean Peninsula and borders North Korea along the Korean Demilitarized Zone, with the Yellow Sea to the west and t ...

through the cities of

Pohang Pohang (; ), formerly spelled Po-Hang, is the largest city in North Gyeongsang Province, South Korea, with a List of cities in South Korea, population of 499,363 as of 2022, bordering the Sea of Japan, East Sea to the east, Yeongcheon to the w ...

Gyeongju Gyeongju (, ), historically known as Seorabeol (, ), is a coastal city in the far southeastern corner of North Gyeongsang Province, South Korea. It is the second largest city by area in the province after Andong, covering with a population of ...

, and

Ulsan Ulsan (; ), officially the Ulsan Metropolitan City, is South Korea's seventh-largest metropolitan city and the eighth-largest city overall, with a population of over 1.1 million inhabitants. It is located in the south-east of the country, neighbo ...

. Notable peaks include Toham Mountain in Gyeongju National Park, as well as Dongdae Mountain itself in Ulsan. The Dongdae Mountains separate the Hyeongsan River basin from the belt of small streams flowing directly into the

Sea of Japan The Sea of Japan is the marginal sea between the Japanese archipelago, Sakhalin, the Korean Peninsula, and the mainland of the Russian Far East. The Japanese archipelago separates the sea from the Pacific Ocean. Like the Mediterranean Sea, it ...

(East Sea).

See also