A year after the death of her husband in 1909, Mary Harriman proposed to Governor Charles Evans Hughes that she would donate 10,000 acres (40 km2) of land and $1 million for the creation of a new state park.

The state agreed and on October 29, 1910, W. Averell Harriman presented a deed for the land and a million-dollar check to the Commission.

In 1913, Major William A. Welch started construction on the road from Bear Mountain to Sloatsburg, known today as the Seven Lakes Drive.

The Civilian Conservation Corps (CCC) offered thousands of young men work such as building roads, trails, camps and lakes.

Projects completed by the CCC in the park included Pine Meadow, Wanoksink, Turkey Hill, Welch, Silvermine and Massawippa Lakes.