The first British survey by the Royal Navy took place in the 1860s. These surveyors named the mountain London Mountain because of the heavy fog and cloud typically gathering around the mountain, but the area informally acquired the name "Whistler" due to the call of the hoary marmot. In the late 19th century, a trail was cut through the valley, linking Lillooet via Pemberton with Burrard Inlet via a pass from Squamish to the Seymour River. The trail was completed in 1877, but because of the difficult and unforgiving terrain, it was only used once for its intended purpose, which was to drive cattle. The area began to attract trappers and prospectors (such as John Millar and Henry Horstman) who established small camps in the area in the early 20th century. The area began to gain recognition with the arrival of Myrtle and Alex Philip, who in 1914 purchased of land on Alta Lake and established the Rainbow Lodge. The Philips had relocated from Maine to Vancouver in 1910, and had heard rumours of the natural beauty of the area from Pemberton pioneer John Millar. After an exploratory journey, the couple was convinced. Rainbow Lodge and other railway-dependent tourist resorts were collectively known as Alta Lake. Along with the rest of the valley bridging the Cheakamus and Green River basins, they became part of British Columbia's first Resort Municipality in 1975.