At first glance, this image looks like a mistake because the gullies of interest are entirely hidden in a large shadow filling most of the crater. At this latitude, gullies preferentially form on pole-facing slopes, but these slopes are in shadow during northern spring and summer.
This image was acquired just after the northern winter solstice, when Southern hemisphere shadows are longest. However, the fine dust in the Martian atmosphere scatters light into the shadows, and HiRISE has the sensitivity to acquire useful images within shadows. [More at link]