I'm not sure. Where I live, in Central Texas, there is a strong German influence, although most of the German emigrants would have come from areas outside of the Alps. Up north around Minnesota, there is a lot of yodeling that's come directly from Scandinavia. I'd say that Cowboy Yodeling may have come into existence when the Scots-Irish "hill-folk" (from whom I and many other people in the Yodel Belt are descended), who used high-pitched "Indian-like" (and possibly also Scottish-influenced) yelps while hunting (not unlike the mysterious "rebel yell"), moved west from the Appalachians. There, they may have met Bavarian, Austrian, and possibly Swiss emigrants who had grown up with yodeling. Also, in the 19th Century, there were traveling families from the Alps who preformed around America, possibly influencing American musicians.

What I'm wondering is the origin of Alpine Yodeling. It's only natural that there would be yodeling in the Alps (yodeling is also found in other mountainous areas like Norway, Persia, Armenia, Georgia, Tibet, Peru, and the Congo)... But who were the first people to do it? Evidence points to either the Celts (Gauls) or the Germanic Tribes, or possibly a pre-celtic people similar to the Basques. Here I'll state the cases for each origin. If anyone has suggestions, please respond.

Celtic origin: Most of central Europe was settled by the Celts for at least 3,000 years. In fact, the La Tene and Halstatt Cultures are both named after places in the Alps. When the Romans and Germanic Tribes began to spread into Europe, they avoided the highest regions of the Alps, which remained a "Celtic enclave" under the Helvetii tribe (Helvetic Confederation being a name for Switzerland). The Alphorn, an instrument associated with yodeling, is very similar to an instrument documented by the Romans when they began to expand into the Alps. This shows that there is still a strong Celtic musical influence in the Alps. As another piece of rather far-fetched evidence, I have noticed that modern Celtic fiddle and bagpipe music follows a similar pattern to some of the more virtuosic and musical Alpine Yodeling. The Scottish Highlanders also used a high-pitched yell in battle (which goes back to what I said about the Scots-Irish and Cowboy Yodeling). But these are probably coincidence because it is unlikely that the musical traditions of the Alpine and Insular Celts have remained that close to each other after being devoid of contact for thousands of years.

Germanic origin: As I alluded to before, there is also a form of yodeling found in Scandinavia, which is also quite mountainous in parts (mainly Norway). Historically, Scandinavia was settled predominately by Germanic (or Germanic-speaking) tribes, who pushed the older Saami (Lapps) and Finns to the arctic and the east. Around 1500 BC, these Germanic Tribes pushed southward into mainland Europe (although they already lived in Denmark and along the Baltic), and eventually came to the foothills of the Alps. It may be possible that this Scandinavian yodeling tendency resurfaced when Germanic-speaking peoples crossed the flat (acoustically deficient) Baltic Plain to find themselves in another mountainous area.

Basque origin: Yodeling can also be found in the Basque regions of the Pyrenees. It is possible that a people similar to the Basques once lived in the nearby Alps, even before the Celts came. Yodeling is probably very, very old, as it was originally used for communication and herding, but not for music. That is one piece of evidence- but it's pretty strong.