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Exposed dikes and sills trending southwest and roughly perpendicular to the primary Koolau rift zone in the Waialae-Palolo area of Oahu are hypersthenebearing tholeiitic rocks, intrusive equivalents of the Koolau Series basalt flows. No Honolulu Series intrusives were located along a line joining Kaau Crater, Mauumae, Kaimuki, and Diamond Head, a secondary rift of the Koolau volcano. Mineralogy of the Koolau intrusives displays a striking chemical and morphological constancy. Feldspar crystals in these rocks show antipathy to ore inclusions. Cumuloporphyritic texture is strongly developed and may be related to flow patterns evident in groundmass minerals.