I found this locally from another bike nut. A 1994 Schwinn prototype frame welded by either Chris Herting or Frank the Welder for pro racer and former world champion Ruthie Matthes. Schwinn was about to break out into the high-end race frame market and sponsored the Evian Water team for that year. These frames preceded the production "Homegrown" bikes by a year and have many Yeti ARC-esque details. Stupid light too at just under 3 lbs. Complete bike with Rock Shox Mag21 SLTi and M900 was around 21lbs.
I took this photo in 1994 at Mount Snow. Racing this very bike?
On a neat little sidenote, I rode this bike on the day of my wedding: