Albedo, rock abundance, and thermal inertia derived from Viking infrared thermal mapper observations provide information about the surface materials within the Mars Pathfinder landing ellipse in Ares Vallis. Relative to the rest of Mars, the site has an intermediate albedo (0.19--0.23), intermediate-to-high bulk thermal inertia (410--540 J m-2 s-0.5 K-1), and high rock abundance (18-25%). At local scales the actual surface distribution of rocks might be heterogeneous, as on terrestrial catastrophic flood surfaces, where rocks tend to be concentrated on fluvially armored surfaces and/or bars. Albedo increases and thermal inertia decreases from the northeast to the southwest in the ellipse, owing to (interpreted) windblown dark sand from Acidalia Planitia. If Mars Pathfinder lands at the southwest end of the landing ellipse, the scene is likely to be the most similar to that of the Viking 1 lander; while a landing at the northeast end of the ellipse is most likely to provide a view that is different from the Viking sites because of low-albedo material. A landing at the center of the ellipse might put the spacecraft near one of two crater clusters that are interpreted to have dark sandy material in or on their ejecta. Aeolian activity during the 30-day Primary Mission might be limited because it is mid-northern summer, a time in which no historic dust storms have been seen in the region, and a season when regional winds should be weak relative to other times during the year.¿ 1997 American Geophysical Union