Kevin,
Interesting question. Difficult to define, maybe impossible. The only influence I can easily identify is the Eisentraut "school". There are many who worked with, or took framebuilding classes from Eisentraut in the early days. More than any other American framebuilder, Albert has been the primary inspiration in style for many. Personally, I was inspired by my Eisentraut in that it was the first low production handmade bike I ever owned and it rode and felt better than everything else I owned including, Italian Masi, Colnago Super, Harry Quinn (custom), Paramount, Pogliaghi, LeJune, and Peugeot. I did not like the lug styling nor the paint jobs, but the bike itself convinced me that careful handmade construction made the best bikes.
I suppose my style is somewhat in the Masi school, as would be Confente Medici, Richard Sachs, and Roland Della Santa. There must be other recognizable styles and sources of influence; but I can't name them off hand. I have strayed (expanded) a bit into other forms that would be more French and English in flavor. I enjoy all styles and would get bored doing everything the same every time. A variety of tastes suit me and at some point (like my double vibrant hellenic frame) the Masi influence is nearly impossible to detect. My full chrome Masi Special Replica on the other hand is quite the opposite!
Geographically, the centers of framebuilding in the US are most frequently close to the locations of long term or larger manufacturing outfits like Masi, Witcomb, Eisentraut, and Strawberry. Often these places are located within areas that have long been cycling centers in the US. So. Cal, Bay Area, Portland, and New England. It seems to make sense. Things get spread out a lot more once you leave the coasts. Trek(in the early days) and Schwinn are about all there is inbetween. I know there are quite a few guys who came through those companies and most are in Michigan or Wisconsin.
Like most things American, our frames are a hodge podge of styles and influences from our brothers abroad in many cases. Isn't that special!
Brian Baylis
La Mesa, CA