We report on a systematic study of gullies and mantled terrain in the northern hemisphere of Mars. Consistent with previous work, the mantled terrain is generally located on poleward-facing slopes, and gullies are found at all orientations. New results are as follows: (1) The range of orientations of mantled terrain increases toward the pole, (2) near-polar gullies are commonly less morphologically developed compared to ones in the temperate latitudes, (3) gullies toward the pole are better preserved than those closer to the equator, and (4) these studies are conducted in the northern hemisphere, whereas most previous work investigated the south. No gully model in the literature cleanly fits all these observations (nor any other gully observations reported in other papers). However, the likely effects of obliquity and precession variations on snow formation, preservation, and melting are consistent with many of the results.