Six major geologic units in Charleston, South Carolina, are characterized in terms of shear-wave velocity (VS) in this article. The characterization is based on in situ VS measurements at 91 sites. The six units are man-made fills, Holocene and late Pleistocene deposits, the Wando Formation, the Ten Mile Hill beds, the Penholoway Formation and the Daniel Island beds, and Tertiary deposits. Median VS values for these units in the top 25 m are 145, 111, 189, 176, 285, and 399 m/ sec, respectively. For Tertiary deposits in the depth intervals of 25–55 m, 55–75 m, and 75–100 m, median VS values are 435, 533, and 663 m/sec, respectively. A seismic-response parametric study is conducted assuming several soil/rock models and two input rock outcrop motions with peak accelerations of 0.3g and 0.1g. It is found that Quaternary sections with VS of 190 m/sec (e.g., the Wando Formation) and thicknesses of about 7 m to 15 m exhibit predominant peaks in the acceleration- response spectra at periods of about 0.25 to 0.4 sec. These predominant peaks match fundamental periods of many existing buildings in the old city district of Charleston. The results suggest that local site conditions contributed to building damage in the 1886 Charleston earthquake.