Contact (marked by arrow) between underlying Mesozoic oceanic basalt (darker color) and unconformable, overlying Penita Formation (lighter color), beach section at mouth of Rio Penita, Burica Peninsula, Costa Rica. In Early Pliocene time, shallow-water marine sediments of the Penita Formation infilled topographic valleys between basalt promontories and hills. Note figures at central right for scale. (1989, photo by Laurel Collins)