Fig. 9. Isochron plot of (1) biotite-hornblende diorite and hornblende-pyroxene gabbro wall rocks, (2) transition rocks, and (3) granitic aplite dikes in the Kernville pluton; see text. Wall rock samples 12-16, dated by Rb-Sr methods are 120.1 +/-5 million years old. The other samples give an average date of 83.3 million years old. Solid circles indicate diorite, sample nos. 14 and 15; open circle indicates sample no. 16 (foliated diorite adjacent to the Isabella pluton). Black squares indicate modified diorite (nos. 33, 40, and 44); squares shaded in the northwest half indicate transition rocks (nos. 34, 38, and 39); and squares shaded in the southeast half indicate migmatized diorite and aplite dike samples in which plagioclase is replaced by microcline and myrmekite (nos. 35, 36, 37, 41, 42, and 43). Numbers adjacent to symbols refer to sample numbers in Tables 1, 2, and 3, and Tables VI and VII in Collins (1988).