There's a fun article in today's Daily Journal that traces the history of the Easton family in Burlingame. I always enjoy reading about the old race tracks, including Shell Park that they built (also called Black Hawk track after the estate name).
Ansel developed a horse ranch on the property. He was only a few miles from another horse ranch run by William Corbett. Corbett had a race track built on his property and, not to be outdone, Ansel had a race track built, Shell Park Course, northeast of the San Francisco and San Jose Railroad tracks (near Highway 101 and Broadway). The crushed shell for the track was taken from the numerous Indian middens (mounds) found along Burlingame creek.
You can read more in the Burlingame Centennial book and the 1876 map on page 50 shows the location. My 1925 map still shows that space as being one big "Easton" block.