Giant volcanoes, canyons, and impact basins dominate the Martian landscape. These features formed one to three billion years ago. They can still be seen today because many of the geologic processes that rework the Earth's surface are either absent or work very slowly on Mars.
Ancient cratered highlands record a period of large asteroid impacts that affected all of the inner solar system. Great geologic changes formed a vast lowland region in the northern hemisphere. Interior processes created a tear in the crust called Valles Marineris, and formed a massive plateau covered by soaring volcanoes in the Tharsis region.
Water flowed for a time, carving river channels and perhaps filling lakes and shallow seas. Slowly, however, the atmosphere was lost to space, the temperature dropped, water became trapped in polar caps and ground ice, and interior heat to drive large volcanic eruptions diminished. For at least the past two billion years, Mars has been a cold desert, where mainly just wind and dust carve the landscape.