From the Santa Cruz State Parks web site:
William Page was born in New York and came to California in 1850 at the age of 18 to try his hand in the mines. He was quickly successful and returned east to his home. He returned again to California in 1852 to work in the gold fields. Although he was unsuccessful in this second venture, he managed to get by. After securing employment with a sawmill in La Honda, he went to Mayfield (present day Palo Alto) and established his own lumberyard.
William Page was a skillful timberland manipulator, and by the end of 1852 he was supplying logs to the mills of the Searsville area, near present day Portola Valley. He built his own shingle mill on Peter's Creek. Trees were selectively logged, and judged suitable for shingles only if they very straight grain so they could be split properly. He later moved the mill to Slate Creek, just east of the present day Slate Creek Backpacking Trail Camp. He established a haul road that connected the mills to the Embarcadero in Palo Alto. This haul road was later named Page Mill Road and still exists today though in a much-improved state.
I was really hoping for more than a sign after hiking for miles, but that is all there is left here -- a flat spot and a sign.
Update 11/17/2024: I camped at the Slate Creek Trailcamp with son and granddaughter. I found that this is the nearest and easiest point to filter water from the creek if you are camped at the trailcamp.