Puʻu o Mahuka Heiau State Historic Site on the North Shore of Oʻahu is the largest heiau on the island, covering 2 acres (8,100 m2) on a hilltop overlooking Waimea Bay and Waimea Valley. From its commanding heights, sentries could once monitor much of the northern shoreline of Oʻahu, and even spot signal fires from the Wailua Complex of Heiaus on Kauaʻi, with which it had ties. It was designated a National Historic Landmark in 1962, when it became the center of a 4-acre (16,000 m2) state park. It was added to the National Register of Historic Places in 1966.