We've known about this gem for a long while now. The fossil was discovered by hikers back in 1935 and later cast by University of California paleontologists in 1948. These were the Dirty Thirties and those living in Washington state were experiencing the Great Depression along with the rest of the country and the world. Franklin D. Roosevelt was President of the United States, navigating the States away from laissez-faire economics. Charmingly, Roosevelt would have his good name honored by this same park in April of 1946, a few years before researchers at Berkeley would rekindle interest in the site.
Both hiking and fossil collecting were a fine answer to these hard economic times and came with all the delights of discovery with no cost for the natural entertainment. And so it was that two fossil enthusiast couples were out looking for petrified wood just south of Dry Falls on Blue Lake in Washington state. While searching the pillow basalt, the Frieles and Peabodys came across a large hole high up in a cave that had the distinctive shape of an upside down rhino.
This fossil is interesting in all sorts of ways. First, we so rarely see fossils in igneous rocks. As you might suspect, both magma and lava are very hot. Magma, or molten rock, glows a bright red/orange as it simmers at a toasty 700 °C to 1300 °C (or 1300 °F to 2400 °F) in hot chambers beneath the Earth's surface. As the magma pushes up to the surface becoming lava, it cools to a nice deep black. In the case of our rhino friend, this is how this unlikely fellow became a fossil. Instead of vaporizing his remains, the lava cooled relatively quickly preserving his outline as a trace fossil and remarkably, a few of his teeth, jaw and bones. The lava was eventually buried then waters from the Spokane Floods eroded enough of the overburden to reveal the remains once more.
Diceratherium (Marsh, 1875) is known from over a hundred paleontological occurences from eighty-seven collections. While there are likely many more, we've found fossil remains of Diceratherium, an extinct genus of rhinoceros, in the Miocene of Canada in Saskatchewan, China, France, Portugal, Switzerland, and multiple sites in the United States. He's also been found in the Oligocene of Canada in Saskatchewan, and twenty-five localities in the US, specifically in Arizona, Colorado, Florida, Nebraska, North Dakota, Oregon, South Dakota, Washington and Wyoming.
We know a bit about him. He roamed a much warmer, wetter Washington state some 15 million years ago. By then, the Cascades had arrived and we'd yet to see the volcanic eruptions that would entomb whole forests up near Vantage in the Takama Canyon of Washington state. He had two horns on his nose and was a distant relative of our modern rhinoceros. He was also a chunky fellow, weighing in at about one tonne (or 2,200 lbs). You can visit the site, but it is one of the most difficult to reach and comes with significant risk. Head to the north end of Blue Lake in Washington. Take a boat and search for openings in the cliff face. You'll know you're in the right place if you see a white "R" a couple hundred feed up inside the cliff. Inside the cave, look for a cache left by those who've explored here before you. Once you find the cache, look straight up. That hole above you is the outline of the rhino.
If you don't relish the thought of basalt caving, you can visit a cast of the rhino at the Burke Museum in Seattle, Washington. They have a great museum and are pretty sporting as they've built the cast hardy enough to let folk climb inside. The Burke Museum is having a bit of a facelift at the moment and is closed while they move their collections to the New Burke, a 113,000 sq.ft. building opening in the Fall of 2019.
