About Gastroenterology of the Rockies
Gastroenterology of the Rockies is a multi-location gastroenterology medical group practice serving the Colorado Front Range from seven clinics across Denver, Boulder, Broomfield, Lafayette, Lakewood, Longmont, and Northglenn. Founded over 30 years ago, the practice has removed more than 300,000 polyps over its lifetime and performs more than 1,400 procedures each year — 72% of which are cancer-screening colonoscopies. Its board-certified gastroenterologists are members of the American College of Gastroenterology and the American Society for Gastrointestinal Endoscopy, and the group operates an endoscopy center, the Hemorrhoid Center of Colorado, and an IBD subspecialty program.
Gastroenterology of the Rockies is a physician-owned gastroenterology group that has diagnosed, treated, and prevented diseases of the digestive tract for Coloradans for more than 30 years. The practice is anchored by a roster of board-certified gastroenterologists — including Dr. Joseph E. Cassara, MD, MBA; Dr. Rohan Clarke, MD, FACG; Dr. Joshua Steinberg (Director of IBD); Dr. David Cristin; Dr. Raul Cubillas; Dr. Natalia Zbib; Dr. Nathan J. Susnow; Dr. David Gatof; and a team of additional gastroenterologists and advanced practice providers — supported by physicians organized by subspecialty (Advanced Endoscopic Procedures & EUS, Complex Liver Disease, IBD, and Pathology). With seven clinic locations along the northern Colorado Front Range in Boulder, Broomfield, Denver, Lafayette, Lakewood, Longmont, and Northglenn, the group offers colonoscopy, EGD (upper endoscopy), capsule endoscopy, no-sedation hemorrhoid banding, advanced treatment for Barrett's esophagus, and AI-assisted polyp detection via the GI Genius module. The group has removed over 300,000 polyps over the lifetime of the practice and performs more than 1,400 procedures annually, emphasizing colorectal cancer prevention as a core mission. Gastroenterology of the Rockies' mission statement is 'To Advance Digestive Health and the Quality of Life for All Our Patients,' and the practice prides itself on a patient-centered care model.
- In business
- Over 30 years (founded c. early 1990s)
- Serves
- Colorado Front Range — Boulder, Broomfield, Denver, Lafayette, Lakewood, Longmont, and Northglenn, CO
- Rating
- Approximately 2.5 stars on Yahoo Local (26 reviews); individual provider ratings available on Healthgrades (e.g., Dr. Joseph Cassara – 22 ratings; Dr. Peter Kaye – 8 ratings; Dr. Rohan Clarke – 6 ratings).
About Gastroenterology of the Rockies
Gastroenterology of the Rockies (gastrorockies.com) has focused on diagnosing, treating, and preventing diseases of the digestive tract for more than 30 years. The group operates seven clinic locations across Colorado's Front Range in Boulder, Broomfield, Denver, Lafayette, Lakewood, Longmont, and Northglenn. Its stated mission is 'To Advance Digestive Health and the Quality of Life for All Our Patients.' The practice emphasizes a patient-centered care model in which physicians and advanced practice providers listen closely, ask questions, and give each patient an active role in decisions about their care.
- Founded over 30 years ago
- Seven Colorado clinic locations
- 300,000+ polyps removed over the practice's lifetime
- 1,400+ procedures performed each year
- 72% of procedures are cancer-screening colonoscopies
Our Providers
The practice is staffed by board-certified gastroenterologists who are members of leading national GI organizations including the American College of Gastroenterology and the American Society for Gastrointestinal Endoscopy. Providers are organized by subspecialty so patients can be matched to a physician with specific expertise in their condition.
- Joseph E. Cassara, MD, MBA
- Rohan Clarke, MD, FACG
- Joshua Steinberg, MD — Director of IBD
- David Cristin, MD
- Raul Cubillas, MD
- Natalia Zbib, MD
- Nathan J. Susnow, MD
- David Gatof, MD
- Simranjit Bedi, DO
- Matthew Seto, DO
- Ramu P. Raju, MD
- Kelly Zucker, DO
- Taimur Khan, MD
- Daus Mahnke, MD
- Timothy Dobin, DO
- Wesley Prichard, DO
- Tamas Otrok, MD
- Elizabeth Nguyen, DO
- Victoria Evelyn, PA-C (Advanced Practice Provider)
- Retired physicians recognized: Steven Chetham, MD; Susan Gieske, MD
Providers by Subspecialty
The practice organizes its gastroenterologists by clinical subspecialty so that complex cases can be directed to the physician best suited to treat them.
- Advanced Endoscopic Procedures & EUS
- Expertise in Complex Liver Disease
- IBD — Inflammatory Bowel Disease (Crohn's & Colitis)
- Pathology
Conditions We Treat
The practice maintains a comprehensive Digestive Conditions Library covering the full range of GI, liver, biliary, and anorectal disorders. The team uses advanced diagnostic tools — colonoscopy, EGD (upper endoscopy), and capsule endoscopy — to identify the root cause of symptoms quickly, and develops personalized treatment plans focused on symptom relief, long-term management, and prevention of recurrence.
- Acid Reflux / GERD
- Colon Cancer
- Liver Disease
- Biliary Diseases
- Varices (esophageal)
- Inflammatory Bowel Disease (IBD)
- Irritable Bowel Syndrome (IBS)
- Achalasia
- Cancer Related to the GI Tract
- Rectal Prolapse
- Colon Polyps
- Celiac Disease
- Anal Fissure
- Barrett's Esophagus
Colonoscopy
Colonoscopy is positioned as the cornerstone service of the practice and is described as the only test that can both detect and prevent colorectal cancer by allowing polyps to be removed during the same procedure. The practice cites extremely high polyp detection rates — contributing to higher survival among early colorectal cancer diagnoses — and uses state-of-the-art tools including the GI Genius AI module to identify polyps that can be hidden to the human eye. Colonoscopy is therefore referred to as the gold standard for colorectal cancer prevention, consistent with American Cancer Society guidance.
- Screening and diagnostic colonoscopy
- GI Genius AI-assisted polyp detection
- Same-visit polyp removal to lower colorectal cancer risk
- Easier prep instructions designed in-house
Hemorrhoid Center of Colorado
Gastroenterology of the Rockies operates the Hemorrhoid Center of Colorado as a specialized service line focused on no-sedation hemorrhoid banding — a treatment that allows patients to avoid sedation while addressing hemorrhoid disease.
- No-sedation hemorrhoid banding
- Co-located with the Lakewood office
Endoscopy Centers
In addition to clinic offices, the practice operates dedicated endoscopy centers where procedures such as colonoscopy and EGD are performed.
- Lafayette Endoscopy Center
- Northglenn Endoscopy Center (11900 Grant St, Northglenn, CO)
Clinic Locations
Gastroenterology of the Rockies operates seven clinic locations along the Colorado Front Range. All offices share the central scheduling phone line 303-604-5000 and fax 720-890-0364. Office hours across locations are Monday – Friday, 8:00 AM – 5:00 PM MST, with a Call Center open 8:00 AM – 6:00 PM MST.
- Boulder Office — 1755 48th St Suite 100, Boulder, CO 80301
- Denver Office — 1830 Franklin Street Suite 220, Denver, CO 80218
- Longmont Office — 1551 Professional Lane Suite 290, Longmont, CO 80501
- Northglenn Office — 11900 Grant St Suite 360, Northglenn, CO 80233 (with Endoscopy Center)
- Lakewood Office — 13952 Denver West Pkwy Bldg 53 Suite 100, Lakewood, CO 80401 (Hemorrhoid Center of Colorado co-located)
- Lafayette Office — 1000 W. South Boulder Rd Suite 200, Lafayette, CO 80026 (with Endoscopy Center)
- Broomfield Office
Patient-Centered Care & Values
Gastroenterology of the Rockies describes itself as a patient-centered care practice. Its providers are trained to listen closely, ask questions, and let the patient have an active say in the care they receive — an approach the group credits with delivering high-quality care and with helping patients throughout Boulder, Denver, Lafayette, Lakewood, Longmont, and Northglenn feel their best.
- Mission: 'To Advance Digestive Health and the Quality of Life for All Our Patients'
- Patient-centered care model with active patient input
- Emphasis on early detection and long-term management
- Patient education integrated into diagnosis and treatment
Contact & Hours
Patients can reach any of the seven Colorado locations through the practice's central scheduling line. The call center is staffed longer than the individual clinics to support appointment scheduling.
- Phone: 303-604-5000
- Fax: 720-890-0364
- Office Hours: Monday – Friday, 8:00 AM – 5:00 PM MST
- Call Center Hours: 8:00 AM – 6:00 PM MST
- Website: https://www.gastrorockies.com/
