After investigating the small amount of Native American and African American genes in my SImpson DNA, it most certainly comes from great-mother Emma Hethcot's family. The Hethcot name had evolved from the name Hathcock or Haithcock, a clan which migrated west from North Carolina.
The Hathcocks had situated themselves along the Virginia and North Carolina border well before the Revolution. They were very clannish and lived in the same communities, and on the same lands owned by their ancestors, for several generations. They were reputedly related to the Saponi, a tribe identified with the Cherokee and the Eno Chicora and other small tribes in the Carolinas.
The Hathcocks were referred to as "Portugese" because of their darker complexions. However, they were more likely "Melungeons", a group of people that were really a racial mix of Europeans, Native Americans, and free African Americans, There are newspaper articles of slave owners suspecting the Hathcocks of sheltering runaway slaves.
While most of the Hathcocks still live in the southern U.S., 4th great grandfather Mark Hathcock moved west from North Carolina to Indiana in about 1805. His grandson, Nathan Wilson Hethcot, moved from Indiana to Iowa and then to Nebraska, where his daughter married Thomas Nelson Simpson.