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Douglas K. Nelson D.O.

Dr. Nelsoon is currently enjoying the retired life. Although he is not treating patients, Dr. Nelson is in our hearts and our thoughts on a daily basis. His presence in the office is missed by the patients and staff but especially by the other providers. As one of the founders of Valley Oak Family Practice , we think it is only fitting that we honor him the best we can.



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. In 2006 she moved to Ojai Valley and joined Valley Oak Family Practice Medical Group.

She enjoys skiing at Mammoth, hiking and mountain biking around Ojai and spending time with her family, friends and her cat.

She also serves on the board of directors of Food for Thought Ojai.  A non-profit organization that works with the local community to support, educate and inspire our school our children and their families to make a healthier food choices.





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Cathy Estill, FNP


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 Bacholor 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 born in Northern California and raised in Santa Cruz. 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.

Dr. Horn completed her residency in Family Medicine at Community Memorial Hospital in Ventura, CA and at Valley Oak Family PracticeMedical Group.  Dr Horn is board certified in Family medicine and Osteopathic Manipulative Treatment. She enjoys seeing a wide variety of patients and takes special interest in preventive health care, geriatrics and women's health.

In her free time, she loves exploring the beautiful Ventura County and the Ojai Valley. Discovering nature and music while enjoying great new food.



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