The Oregon site also exhibits phenomena similar to those perceived by visitors at the mystery spot located outside St. Distorted backgrounds that induce a forced perspective, as with an Ames room. The explanation of the strange phenomena is that they are caused by optical illusions. Oregon Vortex is also famous for 'height change' as the apparent relative height of two people varies, depending on where each stands. Owner Maria Cooper agreed with Donnelly that what people are seeing inside the House of Mystery is an optical illusion but insisted something else was happening outside the house that makes people's height appear to grow and shrink depending on their location. Russ Donnelly, professor emeritus of physics at the University of Oregon visited the Oregon Vortex in 1966 and was convinced it was some sort of optical illusion. James Randi, magician and illusionist, also described the Oregon Vortex (House of Mystery) as an optical illusion in 1998 using photography and mathematics to describe the illusion. They noted similar illusions including the Ponzo illusion, the Zöllner illusion, the Poggendorf and Wündt-Hering illusions. They proposed a framework called 'orientation framing' which describes how the brain's visual processing uses spatial frames of reference. Two UC Berkeley researchers studied the Santa Cruz Mystery Spot and published their conclusions in Psychological Science in 1999.

The same effect can be seen in The Montana Vortex and house of mystery, Pennsylvania's Laurel Caverns, North Carolina’s Mystery Hill, and at Santa Cruz, California's Mystery Spot. Odd angles create an illusion of objects seemingly rolling uphill. The Coopers' daughter Maria and grandson Mark kept the attraction open since then, making it one of Oregon's oldest examples of Roadside Americana. When Litster died in 1959, his wife sold the Oregon Vortex to Ernie and Irene Cooper. When the very similar 'Mystery Spot' was created in Santa Cruz, California in 1939, Litster sued for copyright violations, but withdrew the suit when it was pointed out that he claimed the Oregon Vortex was a natural phenomenon. Litster says he researched the paranormal phenomena of the so-called 165-foot magnet radius. McCollugh convinced his friend, geologist and engineer John Litster to come to the US from his birth place in Alva, Scotland. In 1914, the outpost and assay house were rediscovered by a prospector named William McCollugh. However the building conforms to other purpose-built distorting rooms or 'crazy houses' such as at the Santa Cruz Mystery Spot. The story goes that a gold assay office was built in the area in 1904 by the Old Grey Eagle Mining Company, which slid from its foundation in the early tens, coming to rest at an odd angle. Local legend supposedly states that prior to any construction in the area, Native Americans in the area referred to the site as a 'forbidden' land, and travelers passing through would often find their horses refusing to go through the area.

Oregon vortex