Hi Gary,
Cell phones do work in some places, but not down in the canyons. As for the sheriffs calling Mike, they generally do when there are lost hikers because Mike is experienced in search and rescue, knows the area, and has generally been willing to help when needed.
Another reason why the sheriffs might have called Mike here is because he is the owner of the ranch from which the hikers got lost.
That's all the possible reasons I can see, but some might seek more colorful, conspiracy-theory, hidden motives type reasons. I myself refrain from watching too much television.