The brief descriptions below are designed to familiarize you with our staff's training, professional credentials and work experience.
Keith E Harris, MD
Dr. Harris attended Whittier College in California before earning his medical degree from the Howard University College of Medicine. He completed both his residency in internal medicine and his fellowship in gastroenterology at the Martin Luther king Jr. – Drew UCLA Medical Center. He is board certified in gastroenterology and internal medicine.
Dr. Harris specializes in both diagnostic and therapeutic endoscopy. He has worked as a hospitalist, urgent care physician and an internist.
Dr. Harris joined Mid-Valley Gastroenterology (previously Corvallis Gastroenterology) in the fall of 2014 after having provided gastroenterology services in Roseburg, OR for several years.
Outside of medicine, his interests include fishing, skiing, outdoor activities, and physical exercise.
Chad A Morse, MD
Dr. Morse received his medical degree from Oregon Health Sciences University in Portland, and completed an internal medicine residency at the University of Arizona where he also served as Chief Resident. He went on to Brown University for his gastroenterology fellowship. He practiced in Boise, Idaho for 5 years before relocating to Corvallis in 2012 to be closer to his family.
Dr. Morse is a board certified gastroenterologist and member of the American Gastroenterology Association, College of Gastroenterology, Society for Gastrointestinal Endoscopy and Crohn’s and Colitis Foundation of America. He performs a variety of therapeutic and diagnostic procedures and is dedicated to patient safety, comfort and satisfaction.
He and his wife enjoy the outdoors, including skiing, hiking, and water sports. He also enjoys diving, gadgets, reading and spending time with his dogs.
Greg D Schwartz, MD
Dr. Schwartz completed his undergraduate degree at Wesleyan University in Connecticut before earning his medical degree from the Sackler School of Medicine at Tel Aviv University. He completed a residency in internal medicine at the Albert Einstein College of Medicine/Montefiore Medical Center, where he was named Outstanding House Officer. Dr. Schwartz completed his formal education with a fellowship in gastroenterology and hepatology at the University of Miami/Jackson Memorial Hospital and Center for Liver Diseases. He is board certified in gastroenterology and internal medicine.
Dr. Schwartz specializes in both diagnostic and therapeutic endoscopy. He has been published nationally for his research on capsule endoscopy and small bowel tumors and has a special interest in biliary endoscopy and inflammatory bowel disease.
Dr. Schwartz has been practicing with Mid-Valley Gastroenterology (previously Corvallis Gastroenterology) since 2006. Outside of medicine, his interests include running, playing the drums and spending time with his family.
"I am committed to providing the highest quality of care in both the endoscopic and clinical management of digestive disorders, while maintaining the utmost respect and compassion for the patients of our community."
Surin M Vasdev, MD
Dr. Vasdev completed his undergraduate education at Dulwich College in London, England before entering medical school at the University of London. Upon graduation, he moved to the U.S. where he finished a residency in internal medicine and a fellowship in gastroenterology and hepatology at the prestigious Mayo Clinic before going on staff there. He is board certified in gastroenterology.
Dr. Vasdev has been practicing in Corvallis since 1992 providing patient care in diagnostic and therapeutic endoscopy, as well as general gastroenterology. He founded Mid-Valley Gastroenterology (previously Corvallis Gastroenterology) in 1997 and assumed the role of Medical Director of the Samaritan Endoscopy Center when it opened in 2006. Patient care and satisfaction is of prime importance to Dr Vasdev. He oversees services provided in this state-of-the art facility where the goal is to “provide safe and comfortable endoscopic procedures with cutting edge technology in a facility dedicated to endoscopy”.
Named Assistant Clinical Professor of Medicine in 2007 for Western University of Health Sciences, Dr. Vasdev is actively involved in graduate medical education and teaches students about the gastroenterology specialty.
His other interests include mountain-biking and painting and watching movies with his wife and children.
Matthew M Walton, MD
Dr. Matthew Walton joined Mid-Valley Gastroenterology (previously Corvallis Gastroenterology) in the summer of 2009, after providing care in gastroenterology and hepatology at Dartmouth-Hitchcock Medical Center in New Hampshire.
Dr. Walton earned his medical degree from the Medical University of South Carolina College of Medicine. He then completed an internship and residency in internal medicine, followed by a chief residency. Afterward he remained at Dartmouth-Hitchcock Medical Center and completed a three-year fellowship in gastroenterology. During his chief residency and fellowship, Dr. Walton spent time volunteering at the Good Neighbor Clinic providing medical care and teaching medical students.
As a faculty member at the Dartmouth Medical School, Dr. Walton was honored with the Outstanding Teaching Award in 2005. He is a member of both the American Society of Gastrointestinal Endoscopy and the American College of Gastroenterology. Dr. Walton’s primary areas of interest in gastroenterology include pancreatic and biliary disorders, endoscopic ultrasound and ERCP. He is board certified in gastroenterology and internal medicine.
Dr. Walton was drawn to Corvallis by the vibrant college community, beautiful natural setting and easy access to abundant outdoor activities. He is an avid mountain and road biking enthusiast and enjoys other outdoor recreation including snowboarding, cross-country skiing and backpacking.
Dena M Hulting, PA-C
Certified Physician Assistant Dena Hulting has been practicing with Mid-Valley Gastroenterology since 2007. As a PA, she works closely with the gastroenterologists and clinic staff to provide comprehensive patient care. She sees patients in the office for evaluation, physical exam, treatment, education and follow-up care.
Prior to joining Corvallis Gastroenterology, Dena worked at Oregon State University’s Student Health Services and with a multi-specialty group in Pennsylvania. She earned both a bachelor’s degree and Master of Physician Assistant Studies from Lock Haven University of Pennsylvania. She is certified by the National Commission on Certification of Physician Assistants and is a member of the American Academy of Physician Assistants.
Her personal interests include spending time outdoors and reading.
Johanna R. Peterson, PA-C
Johanna joined Mid-Valley Gastroenterology in 2015 after relocating from Bend, OR. Johanna grew up in Lebanon, Oregon where she attended Lebanon Union High school. She then joined the Air Force and spent 12 years of combined service on both Active duty and in the Air Force Reserve. She attended Linfield College where she majored in Biology and received a Bachelor of Science degree, graduating with honors. She went on to Oregon Health Sciences University where she graduated in 2007 with a Master's of Physician Assistant Studies. Upon graduation, she moved to Bend, OR where she worked in General, Trauma, Colorectal & Bariatric surgery for over 2 years. She then practiced in Urology in Bend for five years.
In her free time she enjoys hiking, camping, boating, travel, and spending time with her husband and 2 young daughters. She is certified by the National Commission on Certification of Physician Assistants and is a member of the American Academy of Physician Assistants.
Kristen H Reeve, PA-C
Certified Physician Assistant Kristen Reeve has been caring for patients in Corvallis since 2004. As a PA, she works closely with the gastroenterologists and clinic staff to provide patients with consultations on a multitude of gastroenterological issues.
Prior to joining Mid-Valley Gastroenterology (previously Corvallis Gastroenterology), Kristen practiced internal medicine at Oregon Health & Science University in Portland -- the same institution where she earned a Master’s of Physician Assistant Studies with high honors. She holds a bachelor’s degree from Oregon State University and is certified by the National Commission on Certification of Physician Assistants. She is also a member of the American Academy of Physician Assistants. Kristen is medically fluent in Spanish.
In her free time, she enjoys tap dancing, outdoor recreation, travel, learning foreign languages, reading and spending time with her husband and children.
Mary K Volcko, PA-C
Mary joined Mid-Valley Gastroenterology after relocating from New England in 2015. Mary earned her undergraduate degree from Union College in Schenectady, New York. Thereafter, she gained years of patient care experience while working in physical therapy at a large hospital in Boston, Massachusetts. She attended Tufts University School of Medicine in Boston, where she earned her Masters of Medical Science in Physician Assistant Studies. She is a board-certified Physician Assistant through the National Commission on Certification of Physician Assistants.
As a physician assistant, she works closely with the gastroenterologists and clinic staff to provide comprehensive care while focusing on patient satisfaction. Outside of medicine, her interests include volleyball, watersports, traveling, outdoor recreation, and spending time with her family, friends, and her dog.
Royce K Ryker, FNP-BC
Royce moved to Corvallis, her husband’s hometown, in 1997 and has worked as a Nurse Practitioner in the Willamette Valley specializing in Gastroenterology since 1999. She joined Mid-Valley Gastroenterology in the summer of 2014.
She earned her nursing degree from Vanderbilt University, Nashville, TN and holds a bachelor’s degree in sports medicine from Willamette University, Salem, OR. She is board certified through Oregon State Board of Nursing and the Accreditation Board for Specialty Nursing Certification.
In her free time, she enjoys volunteering in youth ministries, gardening, and grooming and breeding her Labradoodles.