"These are the markers to send airmail to the Boise area," said Castle, who's a pilot.
Ask Castle and his friend Frank Brady any question about the history of airmail, and they'll likely have the answer.
That includes the story behind the huge arrow on Castle's property.
"They put them in originally for the airmail to go to Boise - this used to be the old highway and it was the tracking system to Boise airport," he said.
Not only does he know about the history of airmail, but he and his friend Frank, know flying too.
"I flew a 210 Cessna, a 172, and an experimental," he said.
Both are pilots.
Castle has been flying for forty-some odd years, long after the big arrows were set in the ground.
"It was the first airmail we had in the United States in the old airplanes and we didn't have the guidance system we have today," he said. "So they put them along the highways and guided the airplanes into the airports."
Back in the 1920's, the United States started the first airmail system.
In those days there were no charts, no radios, and no GPS.
All a pilot had was his eyeballs and arrows that were painted yellow.
Ron's uncle Rex, used the arrows back in the day to fly his airmail routes.
After many calls to historians, KBOI 2News found not a lot of people behind know the story behind the arrows.
But Ponderosa pilot David Molar knows them well.
He says the arrows are located every ten miles from New York to San Francisco.
"Each one just points straight to the next so you just keep finding them," he said.
Pilot Frank Brady said, "I knew it was here, but I didn't know where it was here."
And if you're wondering what Castle's arrow is pointing to, he knows.
"You know where the BSU campus is now?" he said. "That was the BSU airport where the BSU campus is."
Each arrow laid across the country had light beacons that pilots would look for and then followed.
"This is where the tower was at where the beacon light was mounted on," he said.
The arrows have been on Castle's land for more than 90 years and he plans on keeping it together as long as he can.
"I will not let anybody destroy it or move it - it's a historical monument, I feel," he said.
Even though the yellow's faded and the lights are gone, it's not just a big slab to some.
"It's part of our history," he said. "It's part of our aviation history."