Our Executive Staff

Get to know our Leadership Team

Grand Canyon Conservancy has staff at Grand Canyon National Park, as well as spread out throughout Arizona and the United States. We work in a variety of roles in fundraising, educational programs, marketing, strategic planning, accounting, retail, and administrative positions to make sure your support makes a difference.

Theresa McMullan
Chief Executive Officer

Theresa leads the organization’s diverse activities in raising private funds to benefit Grand Canyon National Park, growing earned income streams through operating retail stores within the park, and providing educational and adventure opportunities through the Grand Canyon Conservancy Field Institute. Theresa joined Grand Canyon Conservancy as a board member in 2014 and transitioned to staff in June 2015. As the previous Chief Operating Officer for GCC, she provided oversight of retail operations, human resources, publishing, IT, and facilities management. Through her leadership, retail sales increased 66 percent in four years. She also served as the acting chief financial officer for eight months in 2016. She has worked closely with the NPS staff at Grand Canyon to implement special projects related to major fundraising initiatives and has participated with the park’s Inter-tribal Working Group to further the visitor connection to the 11 associated American Indian tribes to Grand Canyon National Park. Prior to GCC, Theresa was the Vice President of Marketing & Merchandising for SkyMall (the company that produced the in-flight shopping catalog) in Phoenix, Arizona and the co-founder and president of a strategic marketing firm. Theresa is an avid hiker and enjoys exploring the Grand Canyon backcountry.

Marie Buck
Chief Operating Officer/Chief Financial Officer

Marie spent over 20 seasons with ISM Raceway (formerly Phoenix Raceway) as Senior Director of Business Operations, where she helped lead the business through the development of two NASCAR Monster Energy Cup Series events, the return of the Indy Car Series to the circuit, and a $178 million expansion and redevelopment of the facility. She is an active leader in the community, having served on the Board of Directors for WESTMARC and in an advisory role to Raceway Charities, a donor-advised fund to the NASCAR Foundation. Marie grew up backpacking and rafting Grand Canyon with her father, Sven Jarnlof. She is an avid lover of the outdoors and enjoys sharing her passion for Grand Canyon with others. Marie has worked over 20 river trips rowing baggage and guiding customers on Colorado River rafting trips. 


Darin Geiger
Director of Operations

Darin joined Grand Canyon Conservancy in 2018. He brings with him 30 years of retail experience, spanning a wide range of disciplines, including management positions in operations, merchandising, buying, product development, and e-commerce. Darin’s first trip to the canyon was a river trip 20 years ago, and in his free time today, you’ll most likely find him on a trail somewhere below the rim or visiting one of Grand Canyon Conservancy’s eight retail locations to thank the hard-working and passionate staff who serve Grand Canyon’s visitors year-round. "Being involved with a mission-focused organization is extremely fulfilling, both personally and professionally."

Minyin Hart
Director of Finance

Minyin started her career as an auditor with a regional CPA firm in Maryland, specializing in auditing not-for-profit organizations. She attained the position of audit team lead manager for the not-for-profit industry. Through her experience working with various not-for-profit organizations she has gained a deeper insight into the industry, its policies, and business processes. After leaving the auditing field Minyin joined Catholic Relief Services where she collaborated with regional offices around the world to review and analyze consolidated financial statements and ensured quality control over financial transactions and reporting. She is a Certified Public Accountant, Certified Management Accountant, Certified Fraud Examiner, and holds a B.S. in Accounting. Minyin moved to Arizona in the summer of 2019, and quickly became enamored with the spectacular landscapes of the Desert Southwest. She loves traveling with her family, enjoys outdoor activities, and spending time under the dark northern Arizona skies.


Laura Jones
Chief of Staff

Laura moved from Illinois to Grand Canyon in 1995 to enjoy a summer out west. She immediately fell in love with Arizona and decided to make the move a permanent one. After working in the hospitality industry for 14 years, Laura transitioned to Grand Canyon Conservancy hoping for a new challenge working in the rewarding setting of a nonprofit organization. Laura serves as an advocate for the changes that make Grand Canyon Conservancy a stronger partner to the park by leading annual planning processes, strategic initiatives, and special projects critical to GCC’s long-term success. She is an effective facilitator and champion for many critical strategic initiatives involved in growing the organization. "Working for GCC has given me the opportunity to ensure future generations have the opportunity to explore and connect to a place I will forever call home."

Mindy Riesenberg
Director of Marketing and Communications

Mindy first saw Grand Canyon National Park when she was four years old, while moving from the east coast to the west coast with her family, and it left a remarkable impression on her. She has over 20 years of experience as a marketing and communications executive, and has lived and worked across the United States. Much of her career was spent in marketing leadership positions at major art museums, including the Kimbell Art Museum (Fort Worth, Texas), the Walters Art Museum (Baltimore, Md.) and Phoenix Art Museum. Prior to joining GCC in 2017, she worked with the Center for the Future of Arizona and wrote and reported stories for Cronkite News, covering the topics of borderlands and sustainability. Mindy has a B.A. in journalism from San Diego State University and a master’s degree from ASU’s Walter Cronkite School of Journalism and Mass Communication. She has been a featured speaker on the topic of nonprofit marketing for the American Marketing Association, Texas Association of Museums, and Texas A&M University, among others. Currently, she is the the Vice Chair of the board of High Country Humane, and in her free time, Mindy is a professional singer who loves to ski, hike, do yoga, and spend time with her dogs.

Danielle Segura
Chief Philanthropy Officer

Danielle has over 30 years of nonprofit leadership and fundraising experience and brings an extensive background in land conservation, strategic planning, and development. Most recently, she served as Vice President, Chief Development Officer for the Frank Lloyd Wright Foundation, and previously she was the Executive Director of the Mojave Desert Land Trust. During this time, she led the organization through a significant restructuring and growth period, raising individual, foundation, and programmatic revenue and increasing visibility through new, diverse audience opportunities.

Prior to her work at the Mojave Desert Land Trust, Danielle held executive director and development positions at Claremont Graduate University, Idyllwild Arts, and the Blood Bank of San Bernardino and Riverside Counties Foundation. She holds a B.A. in Fine Arts from Loyola Marymount University and an M.F.A. in Fine Arts from Claremont Graduate University. Danielle is on the advisory board of Mil Tree, a veteran’s support organization, and is a member of the Friends of the Mojave Desert Seed Bank and the Association of Fundraising Professionals.

Inspired by her parents, Danielle is a lifelong outdoor enthusiast and had her first Grand Canyon adventure at age five. She is a dedicated steward of public lands and enjoys visiting, volunteering, and celebrating them any chance she can.


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