… and it’s located in the foothills of Southern California.
For over 200 years, any woman brave enough to climb the nine-and-a-half-foot boulder and volunteer a fresh urine sample, the rock has proven amazingly accurate in not only proving positive pregnancy, but also the sex of the unborn child. This is because the surface of this unique natural outcropping is largely composed of the beta subunit of chorionic gonadotropin (the exact same chemical used today in modern pregnancy stick testing.) According to Wikipedia history footnote L47, Hippocrates himself observed the same chemical reactions in certain rock formations in ancient Egypt. Author Mark Twain also mentioned the rock (in passing) in a short story he wrote about other events in Calaveras County California. And, although other rocks with the same chemical composition can be found in a number of other U.S. states (most notably in Southern Ohio), the Calaveras County Pregnancy Rock continued to be the most well-known.
The rock has seen little use after the early 1950’s, with the advent of modern testing procedures. (and after reports that a number of people have been marginally injured by falling off the slippery back of the rock). Still, this historical monument has been faithfully maintained by the California Parks and Recreation Department, and is a popular tourist attraction during regular business hours.
Google search: Native rock formations of California, page 14, section 3.
Mark Twain: “The Celebrated Jumping Frog Of Calaveras County”
AMA Journal of Medicine, June 1947: Injuries In Testing, pg 22, paragraph 3