Cobble of conglomerate cut by a fault, and healed by a quartz vein, Rillito River, Tucson, Arizona


A former undergraduate student gave me this in the 1990s sometime.  I’m 'blanking' on who gave it to me.  She found it in the Rillilto River in Tucson while hiking.  I like the range of history that is bound up in this rock: so many different chapters are preserved.

Age & Formation
The granule conglomerate probably came from Miocene fanglomerate, ~25- 20 Ma. Faulting and vein-filling is probably no older than ~18 Ma.