I've lived in Oregon all this time and I had never heard of
Jump Off Joe in Newport, Oregon. You have to love the internet, because it can answer just about any question you ask of it. Thanks to the United States Geological Survey (USGS) website, I now know that
Jump Off Joe was a sea stack composed of middle Miocene concretionary sandstone of the Astoria formation. I had no idea!
Jump Off Joe was a popular tourist attraction before World War I. It formed a barrier across the beach and forced beach walkers to climb over it and jump off the other side. That, of course, is where it got its name. It was also reputed to play an important role in Native American mythology, but that itself may be mythology.
What's particularly interesting about the USGS site is that it shows pictures of
Jump Off Joe over time and pretty much explains why I have never seen or heard of it. The postcard above shows
Jump Off Joe (the rock formation with the arch in it) in about 1900. By 1910, it already looked drastically different. By 1920, it was severely diminished, and by 1970, it was virtually gone.
See the USGS pictures
here.