The city lies on approximately 200 deep canyons and hills separating its mesas, creating small pockets of natural open space scattered throughout the city and giving it a hilly geography. Traditionally, San Diegans have built their homes and businesses on the mesas, while leaving the urban canyons relatively wild. Thus, the canyons give parts of the city a segmented feel, creating gaps between otherwise proximate neighborhoods and contributing to a low-density, car-centered environment. The San Diego River runs through the middle of San Diego from east to west, creating a river valley which serves to divide the city into northern and southern segments. The river used to flow into <answer>San Diego Bay</answer> and its fresh water was the focus of the earliest Spanish explorers.[citation needed] Several reservoirs and Mission Trails Regional Park also lie between and separate developed areas of the city.
Where did the San Diego River once flow to?
San Diego Bay