San Francisco's shoreline has grown beyond its natural limits. Entire neighborhoods such as the Marina, Mission Bay, and Hunters Point, as well as large sections of the Embarcadero, sit on areas of landfill. Treasure Island was constructed from material dredged from the bay as well as material resulting from the excavation of the Yerba Buena Tunnel through Yerba Buena Island during the construction of the Bay Bridge. Such land tends to be unstable during earthquakes. The resulting soil liquefaction causes extensive damage to property built upon it, as was evidenced in the Marina district during the 1989 Loma Prieta earthquake. Most of the city's natural watercourses, such as Islais Creek and Mission Creek, have been culverted and built over, although the Public Utilities Commission is studying proposals to daylight or restore some creeks.