At approximately mile marker 18.7 on Highway 378, inside Haleakala National Park, turn left onto a short road and drive to the parking area. The rim overlook, at 9,324 feet, provides another superb view of the crater floor.
At one time, Haleakala likely resembled Mauna Loa on the Big Island with its pointed top. But as Haleakala's eruptions diminished and erosion in the early valleys of Keanae (Ko'olau Gap) on the north and Kaupo (on the south) began, they nearly almost merged together near the volcano's summit, splitting Haleakala in two.
There really is no precise historical record of Haleakala's most recent eruption, but an interesting piece of detective work sets it at about 1790. An explorer by the name of La Perouse mapped Maui's shoreline in 1786. He drew a broad, shallow bay between two points on the southwest coast. Combined with another chart of the area, the fact that the peninsula lava flow looks very young, and local legend tells of eruptions at approximately that time, 1790 has since become the most logical date of the last eruption of Haleakala. The area south of the flow is now known as La Perouse Bay, in honor of the man who mapped it. Now is the time to keep your eyes peeled for the spiky silversword. What exactly is a silversword? Read more on our Silverswords of Hawaii article.