Mark West Union School District: A Beacon of Excellence in Sonoma County, CA. Mark West Union School District: A Beacon of Excellence in Sonoma County, CA. Nestled in the heart of Sonoma County, California, the Mark West Union School District stands as a beacon of educational excellence. With a history spanning over a century, this district has been dedicated to shaping young minds and preparing them for the future. It's more than just a school district; it's a vibrant, nurturing community committed to fostering an environment where students can thrive academically, emotionally, and socially.