This beautiful and unique geologic formation of peaks form a stunning natural separation between the once scenic Chorro and Los Osos Valleys. Several hills and peaks cut through the city of San Luis Obispo and the chain runs for 16 miles from Islay Hill southeast of the city to the famous Morro Rock anchored partially immersed in the Pacific Ocean. Although there are nine hills and peaks in this chain of eroded ancient volcanic magma plugs, local residents historically have referred to this chain of peaks as the 7 Sisters, not 9 Sisters. The "7" is in reference to the tallest and most prominent of the peaks, with the lowest and less remarkable smaller hills not warranting inclusion. Paradoxically, a less commonly used moniker by some is the 9 Morros. In that case the smaller, plain, and ''neglected'' sisters are duly acknowledged as members of the family. Most tourists and even many locals erroneously refer to Cerro San Luis Obispo as Madonna Mountain, probably due to its proximity to the Madonna Inn and the large Letter ''M'' that is visible on its eastern flank. The big "M'' actually stands for Mission High School located in town just a short distance from the base of the mountain. Along Hwy 1 a little over midway from San Luis Obispo to Morro Bay, near Canet Road, is the visually striking throne of towering granite known as Hollister Peak. One reviewer here mistakenly calls it ''Johnson Peak'', but there is no peak with that designation in this chain. Enjoy the scenic beauty from the base of these prominences or hike to the summits for breathtaking views but do so only where public trails allow. Some peaks are surrounded by private property or, in the case of Morro Rock, are designated as protected natural habitat for endangered species. Please respect private property and the effort to preserve unique wildlife. read more