Their mother Nancy Adams was with them every step of the way,
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"It was an adventure. We call it our family adventure. It was a journey that we could all experience together, and it was exciting," Adams said.
Mathew and Arabella don't seem to realize just how big an accomplishment reaching the peak of Mount Whitney was, but they do appreciate the nice toys they got when they reached the top.
They got some snacks, too -- a big deal for 4-year-olds.
Their mom says the two have always had a lot of energy, and they love being in nature and the family loves to hike.
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Word of their amazing accomplishments is now spreading in the hiking community and the twins are inspiring others.
Mandy Mejia is training to climb Mount Whitney herself. She heard about the twins on Instagram.
"Look at these kids. They are doing it," Mejia said.
And the inspirational feats for the two are just getting started. Both are already saving up their pennies for the ultimate mountain climbing challenge: Mount Everest.