I came across the North Shore Emergency Association's website recently and found their club history page interesting:
This link briefly discusses how the "travel tone" of 141.3 Hz and the national calling/emergency frequency of 462.675 MHz came to be. NSEA was one of the very first adopters of GMRS in the early 1970s, then the Class "A" Citizens Band. Here's a quick snippet from the link:
NSEA members were instrumental in bringing UHF technology to other public service groups in CB, especially R.E.A.C.T. (Radio Emergency Associated Citizens Teams). Beginning in 1976 key NSEA members spent extensive time meeting with REACT teams in more than a dozen-and-a-half different states, bringing a portable repeater, together with a number of mobile and portable units for field demonstrations...As a result, over 200 personal use repeater systems (all on the same frequency [462.675 MHz]) were set up throughout the United States. In recognition of this trend of explosive growth the Federal Communications Commission formally recognized our frequency [462.675 MHz] as the national emergency and traveler's assistance channel in the Part 95A Rules and Regulations.
Pretty cool slice of radio history!