Figure F54. A. Color close-up of interval 183-1139A-71R-3, 56-69 cm (where the surface has been wetted to accentuate the primary igneous and secondary alteration features). Sanidine phenocrysts in Unit 18 have survived the intense alteration that has affected this flow. B. Color close-up of interval 183-1139A-72R-1, 15-25 cm. Sanidine phenocrysts of Unit 19 have also survived intense alteration. Note the change in phenocryst size from Unit 18 to 19.