On a clear day, they're an unmistakable part of the sky. Most people simply know them as condensation trails off of planes, but there's a growing community of believers who are convinced something more sinister is going on.
Those people firmly believe a classified government project is spraying us with toxic metals.
Despite what others call a lack of firm evidence, they're convinced there are extra planes up there, trying to change our atmosphere. And they're worried it's responsible for trees dying and major health problems.
"Right here you can see these contrails, what I call chemtrails, turning on and off," says Mark as he points to his photos of the streaks in the sky he's taken in Bend over the years. He has dozens of them. "This one was taken in the afternoon, after a very heavy day of spraying."
"I really just see our blue skies gone, to see a constant haze, to taste it, to smell this metallic, sulfur-y taste," says Mark.
That's not his real name. We've kept his real identity secret out of concern by his employer that Mark's passion over the chemtrail theory would hurt business.
"I've heard many times, 'Nothing to see here. Crazy, wacko conspiracy theory.' I've been called that a million times. It doesn't bother me at all."
After moving to Bend six years ago, Mark has thrown himself into researching the chemtrail conspiracy. He's one of thousands believing the government is up to something.
Some think they're spraying to weaken our immune systems. Mark says they're experimenting with global warming by spraying toxic chemicals that are killing our trees and making people sick.
"I do think the weather modification is absolutely part of the program, and it's in the weather modification patents," he says at his Bend home. "There are geo-engineering patents that specifically state these technologies are used to control the weather."
Cloud-seeding is a decades-old practice, with private companies today hired in drought areas to create rain. From the ground or air, for a example a Utah company's website says it releases silver iodide or even compressed liquid propane to bring moisture together to form man-made clouds.
Chemtrail believers say it's all at the expense of human health.
But Central Oregon Community College chemistry professor Carol Higginbotham is skeptical: "As a scientist, I tend to want to look at the data, and I haven't seen anything that persuades me something's going on."
She says what you see in the sky is not a conspiracy at all, but rather contrails made up of a hot engine exhaust of carbon dioxide and water vapor that freezes to leave streaks in high altitudes and cold temperatures.
"If the air is very dry, it may be that the contrail isn't going to persist very long," explains Higginbotham, in her chemistry lab at the college. "If the relative humidity is higher than it might be, that little cloud that forms, the little ice cloud, may be slower to disperse."
The notion that planes are intentionally spraying anything over us is far-fetched and misinformed, according to Central Oregon aviation experts who have been flying for decades.
"In terms of using an aircraft at 36,000 feet to spray into the jet stream, before it ever got low enough to ever do anything it would probably be on the other side of the U.S. or across the Atlantic," says Jerry Bean, an aviation instructor at COCC. "The concentration would be so minute that it wouldn't cause any effect."
Commercially rated, ex-Navy pilot of 40 years Jerry Bean and 29-year Coast Guard helicopter pilot Karl Baldessari are both aviation instructors at COCC in Bend. They say the weight of aerosol sprayers would cost too much in fuel, and it would be a waste of money spent on something that would hardly penetrate the ground. Not to mention the strict FAA flight records.
"It's another check and balance for who's up there," says Baldessari of the documentation planes must file with the FAA. "Where are they going, what are they doing? That's another hurdle to get over when we're talking about a conspiracy operation."
Still, sky-watchers insist it's not flight patterns, but the trails criss-cross and turn to form deliberate grids, and linger too long to be water vapor.
As for Mark's photos showing the trail suddenly stop over the Central Oregon sky, Bean has an easy explanation: "Here in this area, it'd be about the descent point to head into Portland, so they pull the power back -- less heat out of the engine, and as you're descending, you descend out of the contrail."
But theorists like Mark aren't convinced, thanks in part to endless YouTube videos, documentaries and conspiracy websites that back up their theories.
"You can almost guarantee what they're (the government) going to end up saying when they fully admit it, is, 'We're doing it to help you. We're doing it to save the Earth,'" says Mark.
With NASA and the Air Force providing simple graphs on how contrails form, getting to the heart of whether anyone is altering the atmosphere to fight global warming is difficult.
Scientists like Higginbotham say it's a possibility ... for the future. "Those ideas are there and have been there for a long time, but that's a different thing than saying it's happening right now," she says.