Sudbury is divided into two main watersheds: to the east is the French River watershed which flows into Georgian Bay and to the west is the Spanish River watershed which flows into the North Channel of Lake Huron. Sudbury is built around many small, rocky mountains with exposed igneous rock of the Canadian (Precambrian) Shield. The ore deposits in Sudbury are part of a large geological structure known as the Sudbury Basin, which are the remnants of a nearly two billion-year-old impact crater; long thought to be the result of a meteorite collision, more recent analysis has suggested that the crater may in fact have been created by a comet. Sudbury's pentlandite, pyrite and pyrrhotite ores contain profitable amounts of many elements—primarily nickel and copper, but also platinum, palladium and other valuable metals. Local smelting of the ore releases this sulphur into the atmosphere where it combines with water vapour to form sulphuric acid, contributing to acid rain. As a result, Sudbury has had a widespread reputation as a wasteland. In parts of the city, vegetation was devastated by acid rain and logging to provide fuel for early smelting techniques. To a lesser extent, the area's ecology was also impacted by lumber camps in the area providing wood for the reconstruction of Chicago after the Great Chicago Fire of 1871. While other logging areas in Northeastern Ontario were also involved in that effort, the emergence of mining related processes in the following decade made it significantly harder for new trees to grow to full maturity in the Sudbury area than elsewhere. The resulting erosion exposed bedrock in many parts of the city, which was charred in most places to a pitted, dark black appearance. There was not a complete lack of vegetation in the region as paper birch and wild blueberry patches thrived in the acidic soils. During the Apollo manned lunar exploration program, NASA astronauts trained in Sudbury to become familiar with impact breccia and shatter cones, rare rock formations produced by large meteorite impacts. However, the popular misconception that they were visiting Sudbury because it purportedly resembled the lifeless surface of the Moon persists. The city's Nickel District Conservation Authority operates a conservation area, the Lake Laurentian Conservation Area, in the city's south end. Other unique environmental projects in the city include the Fielding Bird Sanctuary, a protected area along Highway 17 near Lively that provides a managed