K-Ar conventional and 40Ar/39Ar ages on plagioclase from altered basalt samples show that Khatchaturian and Rachmaninoff Seamounts in the Musicians Seamounts, north-central Pacific, are 65.2¿2.6 and 86.6¿5.2 m.y. old, respectively. The minimum age of Wentworth Seamount, located on the Hawaiian Ridge near Midway, is 71¿5 m.y. Wentworth appears to be a Cretaceous volcano that was incorporated into the Hawaiian volcanic chain. A single boulder of rhyolite dredged from the northern slope of the seamount underlying Necker Island has an age of 77.6¿1.7 m.y. Apparently Necker is a composite seamount constructed of both Cretaceous and late Tertiary volcanoes. With one possible exception, the ages of these and other Cretaceous seamounts in the north-central Pacific are less than or equal to the age of the adjacent sea floor indicating that the seamounts formed at or near the crest of the East Pacific Rise.