Kaupo is one of the 12 traditional land districts of Maui, and one of eight districts that originate at Pohaku Palaha (Broad Stone) in Haleakala crater, regarded as the center of the island.
A stylized drawing showing the traditional districts of Maui is seen below, with Kaupo in pink at the bottom right.
If the drawing above is overlaid with a satellite image and zoomed in, it results in the image below.
From Pohaku Palaha, the boundary runs down Haleakala, seaward to Kalepa on the eastern boundary. Moses Manu, a noted writer of the 19th century, described Kalepa in this way in the story “Ka Moolelo o Kihapiilani”:
"Iho aku i ka pali o Kalepa. Ia lakou i hiki aku ai ilalo, olelo aku la ke kamaaina i ke alii, auhea olua e na malihini … o ka palena keia o Kaupo a me Kipahulu." (They descended the cliff at Kalepa. As they reached the bottom, the native said to the chief, listen, you visitors … this is the boundary of Kaupo and Kipahulu.)
From Kalepa, the boundary follows the shoreline west to Waiopai. It is important to note that while there is broad consensus identifying Kalepa as the eastern boundary, there is debate as to the western boundary of Kaupo, with some sources placing the boundary further east than Waiopai.
At Waiopai, the boundary turns inland, to the north, running up the steep face of Haleakala to the crater rim. From there, the boundary runs east along the crater rim, and turns north into the crater at the area called Kumuiliahi. The boundary then turns back east inside the crater and ends back at the point of beginning, Pohaku Palaha.
Of particular interest is the amount of area in Haleakala crater that is part of Kaupo, being nearly the entire eastern half of the crater.
Sources:
" Ka Moolelo o Kihapiilani", Ka Nupepa Kuokoa, March 1, 1884 (http://ulukau.org/collect/nupepa/index/assoc/HASH5c8e/b16f4d5f.dir/021_0_023_009_001_01_ful_18840301.pdf)
Sites of Maui, by Elspeth P. Sterling (Editor)