I'm a (hiking) writer and a volunteer with Coconino County Sheriff's Search and Rescue Team, which is based in Flagstaff, Arizona.
Ours is the second largest county in the U.S., including Grand Canyon National Park and the Navajo, Havasupai, Hualapai and Hopi Indian Reservations within its boundaries. Elevations here range from 2,000 feet above sea level along the Colorado River to 12,633 feet at the summit of Mt. Humphreys in Flagstaff, so our Search and Rescue team operates in a variety of terrain and environments, from alpine conditions to desert, mountains and canyons.
If you're interested in joining a Search and Rescue team and are in the U.S., a good place to start is to contact your area Sheriff's Department, since many SAR teams are under their supervision. And if that's not the case in your area, the Sheriff's Office can tell you who to contact. You can also search for a SAR team in the directories on SARStories.com. You can search by state and by country.
Search and Rescue has many different disciplines, including wilderness search, mountain rescue, technical or rock rescue, swiftwater and dive SAR. SAR members participate in body recoveries and evidence searches as well, and some people specialize in K9 and mounted SAR (on horseback).
Most SAR members are volunteers--volunteer professionals, that is, and training is usually provided by the individual units, which will each have their own prerequisites for membership. Some teams have few requirements, such as a minimum age limit and level of fitness, while other teams may have more, like specific medical training. You should inquire with the team you're interested in joining.
Search and Rescue has many benefits for those who participate. Certainly one of those benefits is the satisfaction that comes from helping others. It's also an opportunity to learn and practice many different kinds of skills, including various types of navigation, tracking, rock rescue, and so forth. There are local, regional, and national SAR conferences, where you can take workshops and meet SAR members from all over. Being in SAR is great for those who enjoy some spontaneous adventure and who like being part of a team.
On the flip side, those who join Search and Rescue need to realize that they can be called out any time, day or night, and on weekends and holidays. As volunteers, we respond when and if we're able, but some teams do have a required minimum number of hours per year. Besides participating on missions, volunteers can do things like help maintain equipment and vehicles and other non-mission projects.