References - Nevado de Toluca
Literature

Armienta, M. A., De la Cruz-Reyna, S., and Mac’as, J. L., 2000, Chemical characteristics of the crater lakes of Popocatetetl, El Chichon, and Nevado de Toluca volcanoes, Mexico, J. Volcanol. Geotherm. Res., v. 97, p. 105-125.

 
Web resources
please note that URL of following documents may change. VN doesn't assume responsibility of their up - to date status
CONABIO - Nevado de Toluca
http://www.conabio.gob.mx/conocimiento/regionalizacion/doctos/rtp_109.pdf
CONABIO - Crater Lakes of Nevado de Toluca
http://www.conabio.gob.mx/conocimiento/regionalizacion/doctos/rhp_066.html
México Desconocido - Nevado de Toluca
URL