Mayhew referred to her etchings as "Paintings on Paper" and is given credit for inventing the process today known as Color Monotypes.
During a time-period when it was rare for women to travel alone, Nell Brooker Mayhew drove up the coast of California sketching the twenty one old Spanish missions. In the late teens Mayhew began her studies for her highly regarded California Mission series -- arguably her most famous period of color-etchings. She created more than twenty individual renditions of the California Missions, including Mission Santa Barbara, Mission San Juan Capistrano, and Mission San Juan Bautiste. With her two young daughters at her side, the artist took entire days to sketch each individual mission -- often from multiple views. She would return to her studio to complete the final etchings before printing them in a variety of color themes.
The only architecture-based subjects in her body of work, the compostion of the structures is still firmly rooted around nature. Whimsical trees and bushes seem to crawl up the mission walls -- shrouding the historical buildings with a specifically mystical and lyrical quality.
After many local exhibitions of the Mission series in Los Angeles, the etchings toured the country in national exhbitions. Many were purchased by the Ambassador Hotel in New York City -- which held 94 of Mayhew's pieces in their permanent collection.