El Chaco or Gran Chaco is a region, part of which is in northern Argentina: https://en.wikipedia.org/wiki/Gran_Chaco. The related adjective is Chaqueñan.

Gringo (or gringa, feminine) meaning foreigner often carries a derogatory connotation. However, gringo in Argentina was also used to refer to the non-Spanish European immigrants who first established agricultural colonies in the country.

The Toba are one of the largest indigenous groups in Argentina.

Here is my translation of the sleevenotes from the original LP:

Gringa chaqueña: This is a character without a name, or with many names, who is remembered with respect and affection in that Chaco that they helped to found. They are the ‘gringas’ (women settlers) who arrived when it was "pure tacurúes" (barren land full of termite mounds), Indians and desolation. They went with their men to found a new life, and through their stubbornness and their faith the landscape was transformed. What was desert and hills became a place of work and prosperity. Immigrants yet also Chaqueñans. When they created the reality of today with their own hands and wombs, they stopped being foreigners and become the founders of the province, pride of the country.