New impact craters at five sites in the martian mid-latitudes excavated material from depths of decimeters that has a brightness and color indicative of water ice. Near-infrared spectra of the largest example confirm this composition, and repeated imaging showed fading over several months, as expected for sublimating ice. Thermal models of one site show that millimeters of sublimation occurred during this fading period, indicating clean ice rather than ice in soil pores. Our derived ice-table depths are consistent with models using higher long-term average atmospheric water vapor content than present values. Craters at most of these sites may have excavated completely through this clean ice, probing the ice table to previously unsampled depths of meters and revealing substantial heterogeneity in the vertical distribution of the ice itself.

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Introduction 1.1. Gullies on Mars Gullies are predominantly found within latitudes of ∼30°-50° in either martian hemisphere (Malin & Edgett, 2001), with most gullies in this latitude range occurring on pole-facing slopes (e.g., Harrison et al., 2015). These gullies typically consist of a broad upslope alcove that feeds into a channel, leading to a depositional apron of debris downslope. Numerous mechanisms for gully formation have been suggested: release of liquid water/brine from shallow (