(A) Cross section showing the Pleistocene deposits that underlie the Blackwater National Wildlife Refuge. All ages are in thousands of years (ka). Italicized ages are cosmogenic burial isochrons; underlined ages are radiocarbon ages; all others are optically stimulated luminescence ages. Yellow shading represents Holocene deposits; green shading represents MIS 5 and MIS 3 deposits; shades of red, orange, and blue indicate three distinct paleochannel systems, with depths of western channels inferred from boreholes drilled off the line of section; gray substrate is the Miocene Chesapeake Group. Note break in vertical scale. See Fig. 4B for B–B´ line of section. See GSA Supplemental Data Figures S4 and S5 (see footnote 1) for more detail on sedimentology.