Our caring and compassionate veterinary care team.

Meet the Veterinarians and Team of Geary Veterinary Hospital in Walnut Creek. We’re pleased to provide exceptional veterinary care for your pets. Please call us at (925)-938-8010 to speak to one of our caring staff members.

Dr. Gillian Hamilton


Dr. Hamilton graduated from Mount Holyoke College in Massachusetts with a Bachelor’s of Science degree in Biology (1996) and from Emory University Rollins School of Public Health with a MPH in Epidemiology (2000). Before deciding to become a veterinarian, Dr. Hamilton worked as an epidemiologist at the Centers for Disease Control in Atlanta, Georgia, and then as an infectious disease epidemiologist for the Massachusetts Department of Public Health in Boston. She moved to California in 2003, where she eventually attended UC Davis School of Veterinary Medicine and met Dr. Weiss. After graduating in 2008, Dr. Hamilton completed a rotating internship at San Francisco Veterinary Specialists and then joined the team at Geary Veterinary Hospital, where she stayed for five years before moving to St. Thomas, Virgin Islands. She later returned to California to be closer to family and pursue a future as a business owner.

Dr. Hamilton understands the unique human-animal bond, and in her efforts to provide the best possible care for each individual, she works hard to get to know every client and patient. This new chapter in Dr. Hamilton’s life is especially exciting because she loves being back in California and embracing the challenges of small-business ownership with Dr. Weiss. In Dr. Hamilton’s words: “I’m grateful to Dr. Bjork, who established Geary Veterinary Hospital back in 1979, served so many families and pets for nearly 40 years, and then made plans to hand off the business to us as he eases toward eventual retirement. Dr. Bjork’s leadership has been invaluable, and I look forward to helping build on Geary’s success while taking the business into the future.”

Dr. Hamilton lives in Orinda with her husband and their son, as well as a cat named Flair and a rescue German Shepherd called Roxy. Clients of Geary may have seen her son around the office, where he enjoys chatting with clients and staff, shredding documents, and learning about the business.

Dr. Erica Weiss


Dr. Erica Weiss-Laroche graduated from Bucknell University (Lewisburg, PA) in 1998 with a Bachelor’s of Science degree in Biology. After college she worked in research, analyzing human and veterinary pharmaceuticals and biomedical devices. Dr. Weiss moved to California in 2002, and in 2008 graduated from UC Davis School of Veterinary Medicine. Four years later, she completed a residency in Laboratory Animal Medicine at UC Davis. She began working with Dr. Bjork in 2015 when Dr. Hamilton moved to St. Thomas, Virgin Islands.

Dr. Weiss lives in Vallejo with her husband, who is a physician in Occupational Medicine. He also coaches sled hockey, an adaptive sport for children with disabilities, for the Bay Area Outreach Program (BORP). Dr. Weiss and her husband have a young son, who plays hockey and soccer—and loves scary movies. The family has four Devon Rex cats named Elsa, Ana, Giacomo, and Scooter.

Dr. Weiss’s dream was to own a veterinary practice, and she was thrilled to partner with Dr. Gillian Hamilton whom she met at UC Davis. “Gillian and I got to know each other on our very first day of vet school. I sat down next to her, and we’ve been friends ever since! We feel so fortunate to have gone from friends and study partners to co-owners of a well-established veterinary practice, and we look forward to the journey ahead.” Dr. Weiss has worked with a variety of animal species including cats, dogs, guinea pigs, mice and rats, rabbits, pigs, and sheep.


Dr. David Bjork


Dr. Bjork was raised in Berkeley and attended UC Davis as an undergrad. He graduated from Washington State University Veterinary School in 1969. He returned to the Bay Area after veterinary school and worked in Oakland. Dr. Bjork had the honor of working with dermatology expert, Dr. George Muller at Muller Veterinary Hospital in Walnut Creek. After several years at Muller’s, Dr. Bjork and his wife Kim opened Geary Veterinary Hospital in 1979. Dr. Bjork and Kim have two children who worked with their dad when they were younger. Dr. Bjork and Kim sold the practice in 2018 to Dr. Hamilton and Dr. Weiss. Dr. Bjork sees patients three days a week and follows his passion for skiing the other days of the week. He has one Frenchie named MoMo.

Dr. Nathalie Petersen


Dr. Petersen grew up in Atlanta, Georgia, and spent her summers in rural Michigan, where she developed a love for animals and nature. Her mother (a doctor) encouraged her daughter to choose a career that would allow her to find joy in her work. It only made sense to pursue her dreams of becoming a veterinarian! She graduated from Michigan State University in 2006 with a Bachelor’s of Science degree in Environmental Biology and Zoology. She received her DVM from Louisiana State University in 2011 and has lived in the Bay Area since 2018. Dr. Petersen appreciates the variety that being a general practitioner brings. She is a Contra Costa Veterinary Medical Association board member and is Fear Free and PennHip certified. At Geary, she looks forward to forming lasting relationships with both the clients and their pets throughout every life stage. Outside of work, Dr. Petersen loves spending time with her long-term boyfriend and their three terriers: Maverick, Biff, and Ziggy Stringcheese. Her favorite activities include hiking, running, reading, and traveling.

Dr. Mary Ann Wickes


Dr. Wickes has been a veterinarian at Geary Veterinary Hospital since 2000. She received her veterinary degree from Cornell University in New York and returned to California for an internship at Santa Cruz Veterinary Hospital. She then spent five years in emergency medicine in the East Bay, returning to daytime practice after she started a family. Dr. Wickes and her husband, whom she met at Heather Farm swimming pool, live in Walnut Creek and have three grown children and two young grandchildren (so far). The entire family has been involved with competitive swimming and/or triathlons for many years. Today, Mary Ann is still a member of the Walnut Creek Masters swim team, along with their two local children. Dean and son Greg also coach the UC Berkeley triathlon team. The family has two cats, Oscar and Otter, and two grand-dogs: Doris, a French bulldog, and Tucker, a Golden Retriever.

“After so many years in practice, I still love what I do. Getting to know our clients and helping their pets in the best way I can is what makes my career fun and rewarding every day.”

Dr. Kenichiro Yoshida


Dr. Yoshida grew up in Castroville, California—the artichoke capital of the world!—and started his training as a veterinary assistant throughout his high school and undergrad years. He graduated from CSU Fresno with a Bachelor’s of Science degree, focusing on pre-veterinary medicine. He then worked for several years in biomedical research, where he first met Dr. Weiss. In 2016 Dr. Yoshida earned his DVM from Purdue University.

Dr. Yoshida practiced mixed-animal medicine in Humboldt County before he and his wife moved to the San Francisco Bay Area to be closer to family. He’d like clients to know this: “I’m Fear Free certified, and I’m excited to be part of the Geary Veterinary Hospital team. I will bring my thoroughness, compassion, and care to every patient that I meet.”

In his free time, Dr. Yoshida enjoys baking (his specialties are chocolate chip cookies and sourdough bread), practicing his guitar, playing ice hockey, and catching up on TV shows with his wife on the weekends. Dr. Yoshida completed his first half-marathon in 2021 and is currently in training for his next one. He and his wife like to spend time with their dog (Princess) Leia, who doesn’t understand the meaning of no when asking for scratches and petting.



Clinical Manager

Before she arrived at Geary in 2012 where she started as a client services representative, Karen always knew she wanted to work in a field dedicated to animals. She is the youngest of seven children and grew up with many pets, so her love for animals and her interest in their welfare came at a young age. In 2017, she volunteered to help with animal care at both the Houston Society for the Prevention of Cruelty to Animals (SPCA) after hurricane Harvey and at the Tubbs Fire in Sonoma. While working at Geary Veterinary Hospital, Karen cross-trained to join the patient-care team and went to school to become a registered Veterinary Technician. She has two senior dogs, Niño and Dollie, who are her “special-needs kids, and pride and joy,” as well as two rescues, a German Shepherd (Coraline) and a Lab mix (Athena). As Karen says, “There is so much I like about working at Geary but mostly it’s that all of the people here are like my second family.”


Lead Client Services Representative

Kristin is in charge of scheduling appointments, filling prescriptions, answering phones, and helping to ensure clients get the best care for their pets. She says, “I love coming to work at Geary Veterinary Hospital every day. Whenever I walk through the door, I know I’m surrounded by smart, hard-working, and compassionate people.” Kristin has over five years of experience working in the veterinary field, both in private practice and in shelter medicine. She particularly loves private practice because she gets to follow patients through every stage of their lives. At home, Kristin has two pets: Kittums (an eighteen-year-old cat) and Freckles (a rescued Chihuahua mix who at age thirteen still acts like a puppy). Kittums spent years traveling the West Coast with Kristin and her husband and is never shy about her feelings. She often informs the neighborhood of her mood by loudly meowing in the backyard at certain times of day. Kristin is happy to report that Kittums and Freckles have become best friends, although it took years for that to happen and Kittums still tries to hide it!


Veterinary Assistant Supervisor

Miriam says, “I really love working at Geary Veterinary Hospital. The owners, Gillian and Erica, go out of their way to make sure that every patient’s quality of life is the first priority. All of my coworkers show genuine care for our patients and are always there with a helping hand.” Miriam began at Geary working at the front desk, greeting patients and their owners and prepping rooms for appointments. She has had some schooling at Carrington College in Sacramento in the Veterinary Technician program. A few months after working at the front desk, she began cross-training to work with Geary’s patient care team. She is now a Veterinary Assistant helping to care for patients. Her education, as well as her hands-on experience with animals, has led her to pursue advancing her skills so she can eventually become a registered Veterinary Technician. Miriam and her husband share two beautiful kids and are the proud owners of three cats. Her family loves staying at home but also enjoys outdoor activities such as hiking, bike riding, and camping.

Patient Care Team


Veterinary Technician & Patient Care Specialist

Melissa graduated from Veterinary Allied Staff Education (VASE) and is a registered Veterinary Technician, as well as Geary’s Safety Manager/Coordinator. Animals are Melissa’s passion. “I love client education and interacting with pet owners and pets. After a hard day’s work, I know that I have benefited and improved animals’ lives. At Geary, I love to organize and decorate. Decorating the hospital for the seasons is my thing!” Melissa has a parakeet named Seamus and a fancy goldfish, plus lots of houseplants. She enjoys hiking, exploring, attending car shows, and knitting, and she’s a self-proclaimed tiki fanatic. (She even has a tiki tattoo.) And in case you haven’t heard the news, Melissa is engaged to fellow employee Joel.


Veterinary Assistant

Alfonso—also known as Poncho—joined Geary Veterinary Hospital in 2018 as a Veterinary Assistant. “Funny story: I showed up, thinking I had a job interview. What happened was a different clinic had left me a voicemail that sounded like ‘Interview Geary Hospital.’ Upon arriving at Geary, I said I was here for my job interview and the receptionists looked confused. I realized I was at the wrong place. But I was lucky enough to be interviewed anyhow, and I got the job!” While growing up, Alfonso spent time on ranches and was a member of 4-H, which inspired his passion for animals. He has helped manage livestock herds, participated in livestock showmanship breeding programs, and worked with African Savannah animals at Safari West in Santa Rosa. Before joining Geary, Alfonso worked for a year in Northern Ireland, where he helped promote tolerance and diversity, and traveled to fourteen other countries. He enjoys hiking, dancing, and taking road trips, or simply staying home with his 16-year-old Chiweenie, Spikey. Alfonso also volunteers with a local youth-empowerment organization, One Day At a Time.


Veterinary Assistant

Breanna went to school to become a Veterinary Assistant and has been learning on the job at Geary Veterinary Hospital. She says, “I’ve learned so much here, and it’s been a real pleasure getting to know everyone. I’ve made some great friends and truly enjoy being a part of such an amazing team.” A former dog walker/sitter, Breanna has three dogs of her own: Cali, Buddy, and Duke. She also has a cat named Stanley and two other kitties, Chai and Lilo (a.k.a. L.L. Cool Ranch), that she adopted from Geary clients. Plus, she has a crested gecko. In the past, Breanna owned snakes, lizards, frogs, ferrets, and exotic fish. In her free time, she enjoys playing video games and working on her 2013 Subaru WRX STi (her pride and joy). She and her boyfriend like to go camping in the summer and snowboarding in the winter in Tahoe.


Veterinary Assistant

Nicole (Nic) was born and raised in the San Francisco Bay Area. Because of her love for animals, she has worked with East Bay Animal Rescue & Refuge (EBARR) and performed animal-husbandry jobs at wellness/vaccine clinics, pet-boarding places, and ranches. “At Geary, I enjoy establishing connections not only with our animal patients but also with their human owners. As caretakers and animal professionals, we are these animals’ voices. I will always strive to do my best to help meet the needs of pets and their human counterparts alike.” Nic plans to apply to the Veterinary Allied Staff Education (VASE) program to become a registered Veterinary Technician. In her free time, she loves to hike and take photographs. Her main pastime is taking care of her horse Delilah.

Client Service Representatives


Client Services Representative

Brianna attended College Park High School and is a student at Diablo Valley College, where she majors in the performing arts to pursue her dream of someday becoming an entertainer. According to Brianna, “It’s always been just me and my mom, but I wouldn’t trade it for the world. Our first pet was a cat named Moonlight, who we recently lost, but will always be my baby girl. I also had a mini poodle mix named Beethoven and was lucky to have loved him. My family has recently welcomed two new kittens into our lives, Binx and MooMoo. I’ve run my own pet sitting/dog walking business for over five years now, and it’s a perfect way to get close to lots of animals. Every pet I spend time with is incredibly special. I have past veterinary experience, previously working at an emergency clinic as part of the client-care team. Finding my way to Geary feels like it was meant to be. This is a group who treats each other like family, and that extends to the clients and patients we serve as well!”


Client Services Representative

Kayla is a Communications major at San Francisco State University. In the past, she worked at another veterinary clinic and a pet-supply store—she loves working with animals and their pet “parents” because it gives her the chance to be around people who love their pets as much as she loves hers. Kayla lives in Walnut Creek with her partner, Sophia, and their three cats: Hopper (once a bottle-fed foster kitten), Stella (the sensitive middle child and only girl cat), and Rigel (the oldest and toughest cat on the block). Kayla and Sophia both enjoy fostering cats and kittens, and sometimes have a few staying with them. In her free time, Kayla likes to read, cook, and spend time outdoors. In her words, “I am passionate about animal rescue and welfare, so I like to help where I can. I love working at Geary because I get to engage with clients and talk about the mutual love of their pets. Nothing makes me happier than seeing pets who are well taken care of by their owners!”

Virtual Care Coordinator


Virtual Care Coordinator

Grey began working at Geary in 2018 as a CSR, but now lives in Los Angeles and works with us remotely. Grey is responsible for our online services, including appointment scheduling and client education. In her free time, Grey loves attending baseball games and taking her rescue dog, Raleigh, for walks. Raleigh is a Catahoula Leopard Dog who loves tennis balls and (unfortunately) dislikes humans. Grey’s favourite part of working at Geary is representing something she believes in: high-quality veterinary care from a kind and knowledgeable staff.  In her words, “People ask my opinion of Geary Veterinary Hospital all the time. The most important thing to me is being able to tell them that I believe in the work we do here and that our staff is offering the best possible care.” We are thrilled she can help our clients even when she can’t be here with us in the hospital!