The main difference is that the senita has only four flutes on it arms while the organ pipe has many. The desert environment is very fragile. Slight changes alter the vegetation. Cacti tend to cluster in micro-environments which suit them best. Shown left, the teddy bear chollas are clustered on the lower hillside while the organ pipes are near the top of the hill where it's steeper.
Saguaros tend to favor bajadas, large plains which are gernally flat but mildly sloping.
Amazing forests of saguaros can be found at Saguaro National Park just outside of Tucson, a 90 minute drive from here. Visitors to the area should also check out the the Arizona-Sonora Desert Museum, one of America's top museums. It offers a great collection of desert flora and fauna in a spectacular outdoor setting. The Museum is adjacent to Saguaro National Park. The authoritative guide to outdoor adventure in the wild and beautiful Grand Canyon State.