of commercial development (including golf courses and their fertilizer-rich runoff), the universal use of sewers, and modern sediment retention techniques associated with new development. Visibility runs around 40–50 feet (10–15 m) under most conditions. The water is potable, and many homes along the shoreline run a pipe offshore to provide water during the winter when other water systems may be turned off. The water in the lake is exchanged every eight years, compared to the much deeper, therefore slower, Lake Tahoe, which exchanges every 700 years. The surface elevation of the lake is 152 feet (46 m) above Lake Tahoe. Mature conifer trees can be found on the bottom of Fallen Leaf Lake, preserved for some 800 years by the cold water. Some scientists believe that these trees show evidence of a so-called "megadrought" occurring between the 9th and 12th centuries that eliminated or reduced the lake, allowing conifers to grow to maturity. Even older trees have been identified by dendrologists dating to between 18 and 35 centuries ago. A recent expedition by the Undersea Voyager Project concluded that the ancient trees did not grow there during an ancient drought, but rather slid into the lake during one of the many seismic events that have occurred in the Tahoe Basin since it was formed. After the Tahoe Regional Planning Agency banned two-stroke outboard boat motors in the late 1990s, pollution from these engines was virtually eliminated. Local terrain As the glaciers receded from the Fallen Leaf basin, they left some dramatic rock formations including Cathedral Peak to the west, and the ridge upon which the Angora Lookout is located on the east (now forested). Cathedral Peak () might be better named Cathedral Ridge since, while it appears to be a solitary peak from the vantage point on the lake, it is really the beginning of a ridge that leads in the direction of Gilmore Lake and Mount Tallac. Incidentally, Mount Tallac () is familiar to anyone who was a fan of the television series Bonanza as it appeared with its characteristic cross of snow behind the Cartwright family as they rode towards the camera. Cathedral Peak does not have a trail that leads directly to it, but can be reached by three different approaches. The Middle Trail to Tallac is a trail that begins near Lily Lake and which runs along the northern side of Glen Alpine Valley. It runs