About Us

Welcome to Green Valley Ranch Medical Clinic and Urgent Care Center serving the Green Valley Ranch, Montbello, NE Denver and Denver International Airport communities.

We are committed to providing you and your family with prompt, high quality medical care. We offer a full range of medical services for both adults and children of all ages, on a walk-in basis in our Urgent Care facility (no appointment necessary) and by appointment in our Medical Clinic.

Lab and x-ray services are conveniently available on-site.



  • Get to know the various services available at Green Valley Ranch Medical Clinic & Urgent Care and use the proper services when you need care.
  • If you are unsure, please contact the office first.
  • Arrive on time and prepared for the scheduled appointment.


  • Complete any ordered tests, labs, or visits to a specialist
  • Bring a complete list of your remedies, medications, supplements and vitamins
  • Write down all of your concerns and questions so you remember to ask them
  • Think about actions you would like to take that would improve your health


  • Know who your Care Team at the clinic is
  • Be honest and open about your questions, habits, and symptoms
  • Communicate your thoughts, your concerns, and your needs
  • Ask questions, understand your care plan and who is responsible for what
  • Schedule necessary follow-up appointments before you leave


  • Get recommended laboratory tests, etc. and take medications as prescribed.
  • Request copies of reports, lab work and test results from any other health provider you have seen
  • Keep your appointments as scheduled
  • Follow your care plan
  • Contact your Care Team if you have questions or problems between visits.


  • We value what you think and want to hear your ideas and suggestions.
  • Complete a Patient survey
  • Sign up for our quarterly Patient Advisory Council meeting!
  • Give direct comments to a team member



Augustine Obinnah, MD.

Dr. Augustine Obinnah is Board Certified in Internal Medicine has been practicing medicine since 1994. In Colorado he has served as a County Health Officer and Chief of Medical Staff. He graduated from the University of Nigeria College of Medicine and specialized in Internal Medicine at Saint Barnabas Hospital in New York. Dr. Obinnah is especially involved in the management and treatment of chronic medical diseases including diabetes, hypertension and heart disease. Dr. Obinnah enjoys establishing a strong rapport with his patients. He also enjoys spending time with his family.


<span style="text-transform: capitalize">Karina Tlaxcala-Hernandez</span></br> PA-C

Karina Tlaxcala-Hernandez

Physician Assistant

Karina Tlaxcala-Hernandez, MPAS, is a Board-Certified Physician Assistant who is bilingual in Spanish and English. She is a graduate of the Red Rocks Physician Assistant Program. She holds a Bachelor of Science degree in Biochemistry and minors in Spanish and Mathematics from Regis University. Prior to obtaining her Master’s degree in Physician Assistant Studies (MPAS) she worked as a Clinical Research Coordinator in Obstetrics and Gynecology at UCHealth and Denver Health. In addition to her commitment to deliverIng compassionate patient-centered care, she enjoys cooking, hiking, and camping with her husband and German Shepard pup.

<span style="text-transform: capitalize">Jon Allison</span></br> PA-C

Jon Allison

Physician Assistant

Jon Allison is a nationally board certified Physician Assistant who graduated from Midwestern University in Downers Grove, IL in 1998. He has practiced medicine, as a Physician Assistant, in the areas of Internal Medicine / Urgent care, Cardiology / Critical Care, Gastroenterology / Hepatology. He was also nationally board certified as a Radiologic Technologist prior to becoming a Physician Assistant. He greatly enjoys being outdoors in the rocky mountains and also enjoys hiking, camping, skiing and white water rafting.

<span style="text-transform: capitalize">Karen Elmquist</span></br> PA-C

Karen Elmquist

Physician Assistant

Karen Elmquist, PA-C is a Board-Certified Physician Assistant and graduate of the University of Colorado Child Health Associates Physician Assistant program where she was involved in the Urban Underserved track and participated in a Medical Spanish Immersion program in Costa Rica and Nicaragua. She has a Bachelor of Arts degree in Integrative Physiology from the University of Colorado in Boulder. Karen is a native of Colorado originally from Greeley. She enjoys swimming, hiking, chicken wings, trips to IKEA and empathizing with the Colorado Buffaloes football team (GO BUFFS!).

<span style="text-transform: capitalize">Angela Bryant</span></br>PA-C

Angela Bryant

Physician Assistant

Angela Bryant, PA-C is a Board-Certified Physician Assistant and graduate of Red Rocks Physician Assistant Program. She also holds a MS in Applied Nutrition from Colorado State University Fort Collins and is also a Registered Dietician with 15 years of experience. Angela has served as a Registered Dietician in both clinical and community settings. She enjoys spending time with her family, reading and travelling.

<span style="text-transform: capitalize">Anna Sihon</span></br>LCSW

Anna Sihon

Licensed Clinical Social Worker

Anna Sihon is a Licensed Clinical Social Worker (LCSW) and member of the Mental Health Center of Denver Integrated Care team. As the Behavior Health Consultant/Care Coordinator, Anna provides preventative consultation and brief therapy to patients and their families in English and Spanish. Anna is a former Peace Corps volunteer in Paraguay. She has been working in the social work field for more than 20 years. Anna is an expert in honing in on strengths, gently challenging, and creating a safe environment to grow in. Anna enjoys gardening and hanging out with friends and family.


Ugo Obinnah CPA, MBA

Clinic Manager

The Medical Clinic and Urgent Care practices are managed by Ugo Obinnah. Ugo is a Colorado licensed Certified Public Accountant (CPA) with an MBA in Finance from Columbia University, New York. Her background includes hospital management, consulting and banking. She is a people-person and enjoys her job of ensuring that the business side of the clinics run smoothly fostering a positive patient experience. Ugo is assisted by Jessenia Martinez, MA, Assistant Manager.


In our clinic you may also be assisted by any of our compassionate medical assistants (MAs) – Destani Castaneda, Clara Rios, Sonnia Berumen, Manuela Rios, Wendy Bernal, Melissa Villanueva and Yaricza Sandoval. For your convenience our MAs are bilingual (English-Spanish).