LITTLETON: A New Hampshire woman is believed to be the first person to complete an ambitious hiking challenge in the White Mountains in a single year.

Sue Johnston says she has hiked all 48 of New Hampshire's 4,000-foot mountains in every single month of the year in 2016, the Concord Monitor reports.

The challenge is known as "the Grid" and it takes most hikers years to complete. Completing the Grid requires hiking each mountain in every month, but doing it all in one year isn't required.

The 51-year-old Johnston says December, when she spent 21 days hiking, was her most difficult month.

The state's hiking community tracks the challenge, not the New Hampshire Division of Parks and Recreation.