Herrán was an almost exact contemporary of Diego Rivera, a more famous -- but lesser, in my opinion -- painter. One wonders whether Herrán would have evolved his subjects and style in the direction of Rivera, Orozco, Siqueros and others whose careers spanned the 1930s and often dealt with political subjects.
As it was, his style apparently was influenced by Frank Brangwyn and, to my mind, is similar to many of George Washington Lambert's works. Herrán was an excellent draftsman and his paintings include lines that help define his subjects. In a word, it can be called muralistic. But then, he also painted murals, so it all makes sense.
A study for the paintings below.