Berkeley Mystery Walls

This is a sensationalist article that plays up the "mystery" and old ideas that have since been proven false ("ancient civilizations!"). There has been modern research into these walls, and they date to 1850-1880 when the rush of European settlers arrived clearing pasture for livestock.

[1] http://m.newser.com/story/230029/the-east-bay-walls-continue...

[2] https://en.m.wikipedia.org/wiki/East_Bay_Walls

I think we can safely say the builders were not from Yorkshire, where the workmanship is of far higher quality: https://www.ydswg.co.uk/