Figure F17. Close-up photograph of Sample 183-1137A-29R-2 (Piece 4, 54-62 cm) showing sediment-filled cavity at the base of basement Unit 3. The sediments are a sequence of finely laminated silts/clays, ~1-cm-thick graded beds of fine sands to silts, and a 1.5-cm angular oxidized lava clast with 1.5 cm of attached fine sands to silts. The graded beds fine upward, and the bases are marked by 0.3- to 5-mm-long, tabular silt-clay laminae. Discrete lamina have concentrations of oxidized material (lava). Note the intricately convoluted margin of the lava facing the cavity. We interpret this as an open cavity in the base of the lava flow that was filled by sediments and reworked pieces of lava transported by water moving along the base of the highly permeable lava flow.