The maps were obtained by a Washington, DC-based advocacy group, Public Employees for Environmental Responsibility (PEER), which has for years fought against new telecommunications infrastructure in the first national park in the U.S.
Their release comes just a week after lawmakers in the U.S. House introduced a bill that would allow even more cellphone towers and similar structures on public lands across the nation.
Ken Sinay, who operates the Yellowstone Safari tour company and has been running nature tours in the park's backcountry for two decades, said phone signals became far more prevalent in many parts of the park over the past several years.
His customers typically arrive to get away from modern-day distractions. But some are unable to resist the lure of taking business calls or calling home to check on their dogs.
"It's a real drag at Artists Point," Sinay said, referring to a famous overlook near Yellowstone Falls. "While people are trying to enjoy themselves somebody's on their phone waving their hands and gesturing and walking around in a circle."
Yellowstone technology chief Bret De Young acknowledged the occurrence of "spillover" cellphone signals into backcountry areas, but suggested the coverage maps — released by the park to Ruch's group under a public records request — exaggerated the quality of coverage in parts of the park.
In 2009, Yellowstone issued a wireless and telecommunications management plan that said cellphone coverage "would not be promoted or available along park roads outside developed areas, or promoted or available in any of the backcountry."
"No cellphone service will be allowed in the vast majority of Yellowstone," park officials said in a statement issued when the plan was adopted.
PEER executive director Jeff Ruch said the park had failed to meet those goals and instead ceded its telecommunications program to companies that wanted to offer blanket coverage.
"The ability to disconnect, the serenity value of that, is a park resource that they've given away without a thought," Ruch said.
De Young said it is not the intent to cover backcountry areas, and the park is taking steps to limit cell service as much as possible to developed areas.
That's being done with the installation of new antennas that direct signals more precisely so cellphone services are limited mainly to the small communities and campgrounds in the park.
Two of the park's five cellphone towers now use those specially aimed antennas, and De Young said a third is due to be converted this fall.
A cellphone coverage map provided by the park shows that the signals extend beyond targeted areas but lose signal strength as the distance from the communities and campgrounds increases.
"This will allow the service providers to keep up with new phone technology while limiting unintentional coverage areas," De Young said.
The House legislation introduced last week seeks to encourage even greater cellular and broadband coverage within national parks and other public lands. The measure from California U.S. Rep. Jared Huffman is known as the Public Lands Telecommunications Act.
It would set up an account using rental fees for telecommunications companies with cell towers or other infrastructure on public lands. Money raised would be used by the U.S. Interior and Agriculture Departments to obtain additional communication sites and take other steps to foster greater coverage.
National Park Service spokesman Jeremy Barnum said the agency could not provide an estimate of the number of cell towers in national parks.