Here's the famous and most collected "Lakers", a short term for Lake Superior Agates well known throughout the Midwest states especially Minnesota where most Lake Superior agates have been found. They also can be found in other states like Wisconsin, Illinois, Michigan, Iowa, Kansas, Nebraska and some states along the Mississippi river. They apparently came from billion years old basaltic lava beds of failed Mid-Contiental Rift System that extends all the way to Kansas. The actual age of agates themselves are not known since they could have formed any time after the solidification of basalt lava beds. If they're that old, I would be quite amazed that they're still intact despite hundreds of millions years of weathering. Those agates are really lucky that they escaped the destructive tectonic forces of the active and ever changing Earth.  The only other lucky agates I know of are found at 2-billion years old Pibrara Region of Australia (sorry, the Lakers are not the oldest).
    Red, brown, gray, orange and white seem to be the typical colors of the Lakers even they can include other colors except emerald green and cobalt blue. Alternating bold red and white banding seems to be most desirable of any color combos. Few exposed basalt outcrops had been found in some places such as Brockway Mtns along Keeweenaw Peninsula of Michigan and Michipicoten island.
    The glaciers scrapped the agates from the basalt hosts and spread them over several midwest states and some were carried further by the rivers such as Mississippi River. Even with huge quanitities of agates, good sized agates of good quality are hard to find or it could be just that they're gobbled up by just few experienced agate-finders. Let's not ignore those with diverse and interesting types of plume, psuedomorphs and sagenite inclusions also.

Gravel Pile at Muscatine, Iowa	Sign	How did they miss that One?!	Michigan beach of Lake Superior	Agate!