Tess Geddes

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Tess is Operations and Event Director and co-founder of the Mauna to Mauna Ultra. She is an experienced sports event organizer and ultramarathon athlete. Tess has organized and managed many high profile sporting events throughout the world in stage adventure racing, tennis and golf.

Tess is also a committed race volunteer. One of her volunteer highlights was her time spent working the alpine events at the 2010 Winter Olympics in Whistler, British Columbia.

Tess loves ultrarunning and has competed in many ultra races, including the Marathon Des Sables in Morocco, the Sahara Race in Egypt, the Atacama Crossing in Chile, the Libyan Challenge (twice), the Desafio al Desierto in Argentina, as well as races in France, the Philippines and the US.

Colin Geddes


Colin is Business & Event Director and co-founder of the Mauna to Mauna Ultra. With over 30 years experience in the investment banking and private equity industries, former Managing Director of Deutsche Bank and Founder and Managing Director of ABC Investment Banking.

Colin has a wealth of knowledge which he brings to bear for the development of the Grand to Grand Ultra. He holds an MA Honours (Mathematics and Economics) from the University of Aberdeen and completed the International Management Program, INSEAD and Leadership Development Program, The Wharton School.

He has been married to Tess for 27 years and is an avid sportsman. Colin has worked and done business in over 20 countries with much of that time spent in Asia. He enjoys promoting the event around the world and welcoming the large contingent of overseas participants to the Grand to Grand Ultra, the most spectacular and ambitious endurance event in North America today.

Zac Addorisio


Zac is head of marketing and sponsors for the Mauna to Mauna Ultra. He has been actively involved in the running and endurance sports community for over 20 years. Zac has been involved as an advisor to the management of G2G since its formation and has also volunteered at past G2G events.

As the Vice President and Event Director for an international adventure racing company, he travelled the globe scouting race locations, organizing multi-stage races and supporting thousands of runners to achieve their athletic goals.

Zac has volunteered for and organized numerous local, national, and international sporting events including from the IAAF. As an avid endurance runner himself, he has personally completed numerous marathons and ultra marathons. Through organizing international one-day and multi-day running events on all seven continents, Zac discovered that serving the running community is his true passion. From the novice who is just finding their stride, to the more seasoned athlete who is looking to push the boundaries, every runner has a story.

Josh Mularella


Josh is the Medical Director for the Mauna to Mauna Ultra. He is a board-certified emergency medicine physician and the Director of EMS and Prehospital Medicine for Cambridge Health Alliance in Massachusetts.

Josh was a US Navy medic for 6 years prior to medical school. After his residency training in Philadelphia he completed a year-long fellowship in wilderness and expedition medicine at SUNY Upstate in Syracuse, NY followed by the Diploma of Tropical Medicine & Hygiene in Liverpool, UK.

He is also a Fellow of the Academy of Wilderness Medicine (FAWM). He has published in the fields of EMS and wilderness medicine and continues to be involved in resident/fellow education. Josh has worked at various expeditions and ultra-marathons such as the Southwestern US, the Amazon jungle in Brazil, Cambodia, Sri Lanka and Bhutan. He has been involved with G2G since 2013.

Jeremy Joslin


Jeremy is the Senior Medical Advisor of the Mauna to Mauna Ultra. Jeremy is a board-certified emergency physician with experience and training in the wide spectrum of prehospital medicine from austere wilderness medical support to urban EMS & Disaster response.

As the director of the Wilderness & Expedition Medicine program at the State University of New York, Upstate Medical University, he trains other emergency physicians to provide operational medical support in wilderness & expedition settings while he maintains a research focus in endurance and heat-related illnesses.

He has worked expeditions and events in remote Utah, the Sahara Desert, the Gobi Desert, and the Amazon jungle; and provides ongoing event medical direction for local & national endurance races, as well as other mass-gatherings and events.

Brian Horton

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Brian Horton is the Camp Manager for the Mauna to Mauna Ultra. Brian worked as Assistant Camp Manager for the Grand to Grand Ultra 2016 and thoroughly enjoyed the challenge of creating a temporary oasis in the desert.

When not involved in races, he works as a professional chef. After completing culinary school and a 3.5 year apprenticeship, he went on to work for two James Beard Award winning chefs.

An avid adventurer, he fell in love with ultrarunning. He completed his first 100k in 2016. He combined his passions for food and racing to create his own catering company, specializing in races and backcountry adventures. He is currently based out of Grand Junction, CO where he enjoys exploring canyon country.

Garth Reader

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Garth is the Race Commissioner for the Mauna to Mauna Ultra. Garth is an engineering professional from New Mexico where he manages various emergency response programs at the Los Alamos National Laboratory. Garth began his athletic endeavors at the age of eight when he took up competitive swimming.

After high school he transitioned to triathlons and bicycle racing. While raising his three girls with wife Lisa, Garth continued to keep in the game by focusing on running. This eventually led to numerous marathons, ultramarathons and stage races where he typically finishes in the top ten percent. He also has experience in orienteering, long range shooting, archery, fencing and biathlons. Some notable events he has competed in include the Marathon des Sables (twice) and Ultra Trail du Mont Blanc. 

Garth ran the Grand to Grand Ultra in 2014 and in 2015 he volunteered as one of the main Sweepers. In 2016, Garth volunteered again at G2G in the role of Official Timekeeper.

Stef Hostetter

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Stefanie is our Media Manager. When she is not actively involved in managing our event social media, she is a management consultant who specializes in helping real estate brokerages and small businesses flourish.

She ran the Grand to Grand Ultra in 2012, 2013, and 2015, and volunteered in 2014 and 2016. Stef is passionate about engaging with the G2G/M2M community and she loves helping people achieve their dreams of crossing the finish line.

Sonia Mahoney

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Sonia is the Volunteer Coordinator and Checkpoint Captains Leader for the Mauna to Mauna Ultra. Having spent her formative years in Australia followed by several years in Japan working in public relations, Sonia now lives in Whistler, Canada, sharing her time between her Property Management business, her family, and enjoying life in the mountains.

She is a keen runner, having taken up the sport in 2009 and participating in countless road races. After being introduced to trails and ultra running this became her new passion, and she completed the Grand to Grand Ultra in 2013.

Since then, Sonia has been a dedicated volunteer with G2G, returning every year to be involved in the event. She loves being part of the G2G/M2M family, meeting amazing people from all walks of life, and helping them to achieve their goals.