Provider Directory / B / John Mark Barnett MD John Mark Barnett, MD Oncology Specialties: Oncology Phone Number: 303-684-1900 Fax: 303-684-1925 Website Link: https://www.rockymountaincancercenters.com/physicians/longmont/j-mark-barnett/ Address: Rocky Mountain Cancer Center, LLP 2030 W Mountain View Ave, 210, Longmont, CO 80501 Get Directions