Reef is a term used in Australia and often can be traced on the surface for a great distance.Veins, stringers, are different sizes and cutters intersect the above at different angles and if you can read these cutters in a known gold bearing vein you can often tell when the highgrade ore will appear.Bull quartz the large outcroppings often seen along California's motherlode highways is usually barren or occasionally very low grade rock having been formed before gold bearing solutions arose in our current landscape,but often nearby veins contain ore.Read some good books like Handbook for Prospectors by Von bernewitz or newer editions by Richard Pearl and Prospecting for Gold by the Late great Australian Ion Idreiss.
