These two 1949 definitive stamps of the Republic of Korea depict Mt. Kumgang, or the Diamond Mountains. The 20 won value (Sc #102) was issued on July 1, 1949, and the 400 won stamp (Sc #112) was issued on October 11, 1949.
The Diamond Mountains, in the Taebaek Mountains of the Korean Peninsula's eastern side, now lie in North Korea. From nytimes.com, "No mountain in the Taebaek range is more august than Mt. Kumgang, also called Diamond Mountains: a stunning expanse of jagged granite peaks and coursing waterfalls."