Archaeological sites are often dated through seriation analysis of artifacts found on the site's surface. This relative dating method remains common despite the widespread availability of absolute dating methods because it is fast and cost-effective compared to scientific dating methods such as radiocarbon dating. Surface seriation is especially important for regional survey studies that involve a large number of sites and little to no excavation. In this context it is important to ask: are surface assemblages as reliable an indicator of the age of a site as determined through excavation? This unique study addresses this question using data from seven sites in the Virú Valley on the north coast of Peru. Surface assemblages are compared with excavated ones using the G-test statistic. It is found that surface assemblages do not closely resemble excavated ones in a statistically significant sense. Nevertheless, the relative date of surface assemblages typically resembles the relative date of excavated assemblages. Caution is urged when dating surface assemblages purely through seriation because the surface may not actually be representative of excavated assemblages.