Our Providers
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Maria L. Halvorson
D.O.
Dr. Maria Halvorson grew up in Ojai, CA and graduated from Nordhoff High School in 1989. She attended the University of San Diego where she received her Bachelor of Science degree in Anatomy and Neuroscience. She received her Doctor of Osteopathy degree from the College of Osteopathic Medicine of the Pacific/Western University of Health Sciences in Pomona, CA. She completed her Osteopathic Family Medicine Residency program at Eastmoreland Hospital in Portland, Oregon.
She returned to Ojai and joined Valley Oak Family Practice Medical Group in 2001.
She enjoys hiking, training for triathlons and spending time with friends and family. She is very happy to be living in the community in which she practices medicine.
Helen Petroff
M.D.
Dr. Helen Petroff was born in Los Angeles, CA and grew up in Fullerton, CA. She received her Bachelor of Arts degree from Princeton University in Princeton, NJ. She received her Medical Doctor degree from University of California Irvine. She completed her Family Medicine Residency through the University California Los Angeles in the Northridge Hospital in the San Fernando Valley.
She moved to Ojai and joined Valley Oak Family Practice Medical Group in 2006.
She enjoys skiing at Mammoth, hiking and mountain biking around Ojai and spending time with her family, friends and her cat.
Cathy Estill
F.N.P.
Cathy Estill has been a resident of Ojai since 1952 and grew up on Hitching Post Ranch, the land on which the Ojai Valley Community Hospital, Nordhoff High School and the "Y' now stand.
Cathy earned her Registered Nursing degree from Ventura College in 1969. After practicing nursing for several years in the Ojai valley she furthered her education at California State University at Dominguez Hills where she received her Bachelor of Science of Nursing degree in 1991. She then went on to attend the University of California Los Angeles Graduate School of Nursing where she earned her Masters of Science in Nursing/Family Nurse Practitioner degree in 1996.
Cathy has been able to spend her entire working career caring for the people in her community.
Natalie Horn
D.O.
Dr. Natalie Horn was raised in Santa Cruz, CA. She received her Bachelor's of Science degree from the University of California Santa Cruz. She attended Western University of Health Sciences in Pomona, CA and received her Doctor of Osteopathic Medicine degree.
She completed her residency in Family Medicine at Community Memorial Hospital in Ventura, CA. Prior to medical school she worked with the UCSF HIV/AIDS Health Project.
Dr. Horn chose family medicine early on in her academic journey because of the wide variety of patients it allows her to care for. She finds joy in the doctor patient relationship and seeing everyone from newborns to 100 (and beyond) year olds!
In her free time, she enjoys adventures in food, nature and music. She loves exploring beautiful Ventura County, Ojai Valley and beyond with her husband and dog in their vintage camper.
Michelle Griffith 

F.N.P.
Originally from Pennsylvania, Michelle moved to Ojai with her husband in 2016. She received a Bachelor's Degree in Neuroscience from Kings College, Wilkes-Barre PA. While working in stroke research she obtained a Bachelor's degree in Nursing from Penn State University where she worked as a Neonatal Intensive Care Nurse at Childrens Hospital of Philadelphia. Michelle completed her Masters of Science in Nursing at Maryville University. She did her clinical training at Community Memorial Hospital and Valley Oak Family Practice. Michelle takes special interest in newborns, weight management, joint pain, and preventative care. In her spare time Michelle enjoys spending time with her family exploring the outdoors.
Kristyna Fong
D.O.
Dr. Kristyna Fong is a kind-hearted Chinese-Filipino American from Las Vegas, Nevada. She studied Biology and Chemistry at the University of Miami in Florida and completed medical school training at Western University COMP-NW in Lebanon, Oregon. In 2019 she traded in gray skies for sunnier weather and completed her family medicine residency at Community Memorial Hospital in Ventura. She joined VOFP in 2022 and is honored to serve the Ojai and Ventura community.
Dr. Fong strives to practice a root-cause approach and encourages healthy habits to maximize quality of life across a lifetime. She is grateful to call California home and enjoys an abundance of outdoor activities; most recently, pickleball, yoga, snowboarding and walking her dog. She and her husband are thrilled to welcome their first child into the world this year.
Wallace Baker
M.D.
Dr. Baker received his B.S. in biology from Pennsylvania State University and stayed for a Master’s of Science in Exercise Physiology. After his Master’s he attended Temple University Medical School in Philadelphia, graduating with Honors. During his training, he developed a great curiosity and respect for all aspects of medicine and a commitment to the doctor-patient relationship. These passions guided him toward a residency in Family Medicine at the Ventura County Medical Center in Ventura California. After graduation, he worked for 7 years in a small-town family medicine practice in Ithaca New York, and then he joined the Core Faculty at the Ventura County Medical Center Family Medicine Residency Program. On the faculty for 10 years, he served as the clinic Medical Director and the Director of Global Health. His current areas of interest are lifestyle and preventive medicine and general internal medicine. His approach to patient care emphasizes treating the whole patient to maximize the quality and length of the health span in the context of their environment. Dr. Baker also specializes in tuberculosis treatment at Ventura County Public Health.
In his free time, he enjoys time with family and friends, traveling, gardening, cooking, hiking, and any time outdoors. Dr. Baker fully appreciates the people and unique beauty of the area we call home and he is very happy to be part of the Valley Oak Family Practice team.
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Nicole Kehoe
M.D.
Dr. Nicole Kehoe joins Valley Oak Family Practice Group in April 2024, continuing her mission to provide attentive, comprehensive, and compassionate care to diverse patients of all ages — newborns to seniors — with a focus on health maintenance and prevention. She has a strong professional focus on women’s health, family planning, and teaching. She is known for developing long-lasting, caring, and healing patient relationships. Dr. Kehoe is fluent in Spanish.
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Born and raised in southern California, Dr. Kehoe graduated from Yale, where she played
volleyball and garnered Academic All-American honors. She earned her medical degree from the University of California, San Francisco, and was inducted into the Alpha Omega Alpha Honor Medical Society. She also did volunteer and clinical work, learning from both western physicians and traditional healers, in Bolivia, Ecuador, and Guatemala.
She completed her residency in Family Medicine at the University of Washington, Harborview Medical Center in Seattle. Board-certified in Family Medicine, Dr. Kehoe is a member of the American Academy of Family
Physicians.
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Dr. Kehoe is married with two children and lives in the Ojai valley. She enthusiastically cheers on her children at sporting events and school performances. Dr. Kehoe loves spending time outdoors, traveling, and baking.
