(CNN) -- Native Americans on the rugged Navajo and Hopi reservations in northern Arizona are using mirrors and red fabric to signal aircraft that they need air drops after last week's powerful snowstorm, state agency spokesmen said Wednesday.
Drops of food, water and medicine are being made in Coconino, Apache and Navajo counties, which spread out over 20,000 square miles, Eric Neitzel with the Division of Emergency Management told CNN.
Most of the territory belongs to the Navajo Nation, which surrounds the Hopi Reservation.
The reservations make up 21 percent of the state, he said, or nearly all the land north of Interstate 40 and east of the Colorado River. The Navajo Nation also extends into New Mexico, Colorado and Utah.
Neitzel said at least four medical evacuation missions had been made by midday. Some had been for people needing dialysis treatments.
He said the missions could continue for at least another week.
Snow showers that are predicted through Thursday could severely hinder rescues and food drops, Neitzel said. Dozens of roads remain closed.
Flagstaff, in Coconino County just southwest of the Navajo Nation, posted its second-highest snowfall of 54.2 inches over seven days, the National Weather Service said.
On Monday, President Obama declared a state of emergency for Arizona, allowing agencies to use federal money for rescues, supplies, transportation and crews.
The mission is being run like a wildfire response.
The emergency management division contracted with the U.S. Forest Service to use an Air Attack plane, Neitzel said. The plane, often used in firefighting, finds people who need supplies and reports back so helicopters can do air drops.
The reservations, Neitzel said, are on mostly rugged, mountainous land, and most of the people live at higher elevations. Their homes are very difficult to see from the air.
Agencies are now on a mission to provide coal for heating and firewood for cooking, as temperatures dip to single digits overnight and hover in the 20s and 30s during the day, Neitzel said. Teams began doing preliminary damage assessments Tuesday.
The Navajo Nation has a population of about 175,000, and the Hopi Reservation, nearly 7,000. Many households lack electricity and telephone service.
"It's a pretty serious situation out there," Neitzel said. "We are relying on ground intelligence [gathered by the Air Attack planes] to get us where we need to go."
Dozens of personnel from the emergency management division, the Civil Air Patrol and local governments have helped pull people out of the snow, said the division's Ethan Riley. He said the agency, aware that the snow was coming, prepositioned supplies and some National Guard troops.
The bad weather began January 18, peaked with a major storm Thursday and continued through the weekend. A pilot flying over the area reported that with the help of high winds, there was snow up to some rooftops, or more than 8 feet.