Yeongju City's
I-san Heukseok-sa
영주시 이산면 흑석사
黑石寺  Black-Rock Temple
Korean Treasure #681 -- Stone Seated Buddha with Relief-carved Buddha-Triad Nimbus-Boulder, from the 800s CE
National Treasure #282 -- Wooden Seated Amitabha Buddha and Excavated Relics from inside it
This was created in 1458 during the reign of Joseon King Sejo as the Principal Buddha of the Triad of "Beopcheon-sa Temple"
From my Encyclopedia of Korean Buddhism:
Amita-bul  아미타불  阿彌陀佛 -- Amitabha the Buddha of Western Paradise
The Buddha Amitabha, manifestation of the aggregate of discrimination of all Buddhas, and believed to be an infinitely
compassionate immortal Buddha who presides over a celestial paradise or Jeongto (淨土, Pure Land). located in the Western
Heaven and therefore often called the “Western Paradise”.  He is the main object of veneration for the Jeongto-jong (淨土宗,
Pure Land School). A very common deity in Korean temples, often in his own Geungnak-jeon (極樂殿, Extreme Bliss Hall,
Paradise Hall or Amitabha Hall), also sometimes entitled Muryangsu-jeon (無量壽殿, Immeasurable Life Hall) or even just
Amita-jeon (阿彌陀殿). His icons may also be found in other temple Halls, perhaps as part of a triad with other Buddhas or
Bodhisattvas.
      He is frequently depicted above the main altar of a Geungnak-jeon in a Geungnak-hoesangdo (極樂會上圖, Paradise
Assembly Painting) depicting the Western Paradise. In front of that is enshrined a seated statue of Amita-bul, flanked by two
Bodhisattvas; this arrangement is called an Amita Samjonbul (阿彌陀三尊佛, Amitabha Triad). Amita-bul usually performs the
teaching mudra or 1 of 9 meditation mudras, with the precise arrangement of the fingers indicating one of 9 grades of rebirth.
      Because of Amita-bul's compassionate nature, all that is required to be reborn in his paradise is the devout recitation
of the simple phrase, “Namu Amita-bul” (南無阿彌陀佛), which means “Homage to (or taking refuge in) Amitabha Buddha”,
according to the Jeongto School.  This appealingly uncomplicated form of Buddhist belief was introduced to Korea during
the latter part of the Three Kingdoms Era and became tremendously popular during the Unified Shilla Dynasty period.  
The explosive growth of the cult's popularity in Korea during the 7th through 13th centuries parallels its developmental
course in China and is directly reflected in the surviving corpus of Korean Buddhist sculpture.  Records of extant Korean
statues indicate, for example, only one Buddha image identified as Amita-bul dating to the Samguk-sidae and five dating
to the Unified Silla Dynasty period.
Sacred Relics found inside this statue
Sanshin Statue
Sanshin relief-carving on a boulder
seen with the Sanshin boulder-carving behind it (see that below)