The stratigraphic relation between the Sespe and Alegria formations consist of a gradual facies change from the terrestrial environment of the Sespe to the marine environment of the Alegria. Detailed columnar sections show the gross lithologic members within the two formations. Individual members lose their identity laterally over the relatively short distance of approximately a mile or less, with changes in lithology, texture and color, or a combination of these, and exhibit much thinning, wedging and grading. The major lithologic units recognized within the two formations consist largely of cobble and pebble conglomerate, fine-, medium- and coarse-grained sandstone, siltstone, and mudstone.
The red pigment (Fe2O3) which colors several members within the Sespe and Alegria formations is dispersed throughout the clay complex of the finer-grained sediments. The rapid burial of these sediments before alteration has thus preserved much of the original red coloration. The presence of organic matter at the site of deposition caused reduction and the initially red sediments transformed into drab-colored deposits.