El Salto de Los Trexos and the surname "Si"

I have ancestors with the last name "Si" also attached to the last name of Trexo (Trejo} from El Salto de Los Trexos, Tlaltenango Sanchez Roman.

Two questions:

1) Is the last name "Si" Chinese? This surname first appears attached to Jose Tomas Trejo Si, born in 1807, whose parents were Jose Antonio Crecencio Trejo Robles and Juana Maria Si.

2) Was there a large ranch whose name was El Salto de Los Trexos within the Tlaltenango?