This study quantifies uncertainty in Central and Eastern North America (CENA) Reference Rock (RR), Weathered Zone (WZ), and resulting earthquake ground surface site response predictions. The assumptions used for modeling the WZ have an effect on the predicted ground surface response. Random modeling of the RR and WZ is implemented using a simple Taylor Series expansion. Equivalent linear site response analysis is performed with a synthetically generated motion and includes the site attenuation parameter, kappa (κ), for modeling site damping. Probabilistic site response spectra and ratios of response spectra are presented. This study introduces a simple method for quantifying uncertainty in ground surface response while capturing RR and WZ variability.