Tristan Foison emigrated to the USA at the end of the 1980s so it seems. He settled in Atlanta (Georgia) and it did not take very long to find a place in the local classical music scene. For example here the title page of a concert on 8 May 1991 at the Georgia State University Concert Hall presented by the Living Composers, Inc. (a union of Georgia-based composers). Tristan Foison (the third from the right) already in the front row:
Tristan Foison soon established himself as one of the most interesting musicians in Georgia. In 1995 he was appointed principal conductor of the Rome (Georgia) Symphony Orchestra, a professional orchestra and on of the oldest in the USA. Here Tristan Foison on the title page of a concert programme for the season 1997/98: