What two martian features suggest that water once existed on its surface?

Two Martian features that suggest water once existed on its surface are valley networks and outflow channels. Valley networks resemble river systems on Earth, indicating that liquid water may have flowed across the surface, carving these formations. Additionally, outflow channels, which are large, wide depressions, suggest that massive amounts of water were released rapidly, likely from melting ice or subsurface reservoirs, further supporting the presence of water in Mars' past.