The Sphinx is depicted two more times in the book.
> Little did they know...
Mark Twain visited the Sphinx in 1869, its body had already been largely excavated about 50 years before.
His book is really good as well, he has good details of history a lot of people never pay attention to and he has a great sense of humor that keeps everything interesting.
In The Path of Destruction by former USGS geologist Richard Waitt. Incredible compendium of eyewitness accounts of the 1980 eruption.
Amazon: https://www.amazon.com/Path-Destruction-Eyewitness-Chronicles-Helens/dp/0874223237
WSU Press: https://wsupress.wsu.edu/product/in-the-path-of-destruction/