About Us
At El Potrero Chico Guides, we're committed to providing you with a thrilling and unforgettable adventure. Our parent company, Sierra Climbing School LLC, has been in the business for years, and we are proud to be owned and operated by an AMGA certified rock guide, Mark Grundon. We believe that it is important to have the highest trained and most knowledgeable guides in the industry, so you can have an enjoyable and safe experience climbing the incredible Potrero Chico.
Mark Grundon
Mark has been guiding from Alaska to Colorado for the last 16 years. He also currently splits his time between Yosemite National Park and El Potrero Chico. He also guides trips on Mexico's volcano Pico de Orizaba. He recently retired from ski patrol after seven winters to follow his deeper passion: climbing. Mark is a strong believer in “living the dream”, and following your passions whatever they may be. Mark enjoys sharing a rope with everyone from Yosemite rock stars to first time climbers. He has guided 7 successful summits of El Capitan. He has made one day ascents of El Cap and Half Dome in Yosemite. Mark has his EMT, a Leave No Trace trainer certification, is an Assistant AMGA Single Pitch Instructor Provider, AMGA Apprentice Alpine Guide, and AMGA Certified Rock Guide.
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Garet McMackin
Garet is an AMGA Assistant Rock Guide, Single Pitch Instructor, Wilderness First Responder, and former Marine. He has guided and climbed extensively throughout California, the Southwest, the Pacific Northwest, and Mexico. He currently lives and guide's in his favorite place on earth, Yosemite Valley, and has climbed most of the classic routes in El Potrero Chico. Garet brings sound judgment, strong technical skills and a calm safety, first mindset to every objective. When he's not guiding or climbing, Garet can be found exploring Baja, the Sierra Nevada, and beyond with his partner Rachel.
Chris Brey
Chris is an AMGA certified Rock Guide, Nationally Registered EMT, and Wilderness First Responder. Chris is from California where he has guided in some of the areas most iconic venues including Joshua Tree, the Southern Sierra, and Yosemite. He brings a calm, confident presence to the vertical world, combining technical expertise with a passion for teaching. Whether introducing new climbers to their first routes or refining advanced systems with seasoned experts, Chris creates a supportive and educational experience rooted in safety, efficiency, and respect for the mountains. Chris is excited to share El Potrero Chico's world-class limestone and vibrant climbing community with guests from around the world.
James Gustafson
Having been born and raised in Alaska, James has a great appreciation for the outdoors. He has been guiding since 2011 in Alaska, Colorado, Utah, Nevada, and California. His favorite type of climbing is long alpine rock objectives. In the off season James can be found traveling around the US guiding rock, ice climbing, and spending his personal time in the mountains. James has multiple one day ascents of El Capitan, and successful guided ascents of El Capitan. James is an AMGA Certified Rock Guide, Wilderness First Responder and Leave No Trace Trainer.
Lani Chapko
Lani is an AMGA Certified Rock Guide from Index, Washington. She has spent the last 5 years climbing and guiding all over the West Coast of the US. A love of mixing climbing and travel has taken her to Ecuador, Argentina, Chile, Nepal, Mexico and Canada. She enjoys all forms of climbing but finds her fullest expression of the sport to be on long adventurous routes and big walls. She has put up first ascents in Washington and Red Rock. Lani has a degree in engineering, and enjoys nerding out about gear and systems. She is also AMGA Assistant Alpine Guide, Wilderness First Responder, and Leave No Trace Trainer. Lani loves sharing the sport that has brought her so much joy with others. Looking forward to getting to know you in the great outdoors!
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Sam Boyce
Sam grew up in the foothills of Washington state, in the heart of the Pacific Northwest. Here, he developed a keen sense of adventure and stoke for anything climbing. Sam's specialty is in the world of Big Wall climbing. He has climbed dozens of big wall routes including numerous ascents of El Capitan, ranging from 1 day to 8 days. His passion is adventure climbing, and in particular doing first ascents. He has pioneered new routes of every style, from single pitch sport climbs, to big bold trad lines hiding in plain sight, to heavy duty backcountry big wall aid climbs. He started instructing and guiding in 2015 and has worked full time as a Rock and Alpine guide ever since. Sam is a Wilderness First Responder, a Leave no Trace Trainer, is a Certified AMGA Rock Guide, and an AMGA Assistant Alpine Guide.
Adam Mitchell
Adam has been guiding in El Potrero Chico for years. He is an AMGA Rock Guide and will be taking his exam soon. He is an AMGA Single Pitch Provider and runs a climbing school in Texas at Enchanted Rock.
