Images from the High Resolution Imaging Science Experiment have revealed new details on the morphologic and topographic characteristics of slope streaks on Mars. Over 1500 HiRISE images were analyzed with 78 unique image sites having slope streaks. Images with low sun illumination reveal that dark slope streaks have topographic relief where streaked surfaces are lower than their surroundings. Slope streaks often initiate below localized features such as rock outcrops, individual boulders, and impact craters. They are also abundant in great numbers within the blast zones of small young impact craters 10–50 m in diameter. These observations suggest that slope streaks can be triggered by localized disturbances such as rockfalls and impact blasts. Seismic activity from external (e.g., impacts) or internal forces could also trigger slope streaks. The topographic relief and triggering mechanisms of slope streaks seem to best fit models that involve dry dust avalanches. Martian slope streaks and meters-thick avalanche scars are part of a continuum of active mass-wasting features at meter to sub-meter scales.