The next year she went to South America and travelled by canoe down the Amazon River, covering 4,800 kilometers in two and a half years, ending at its source in the Andes. This expedition resulted in 65,000 specimens. On that expedition she spent three months living with the Araguarunas, a native group in the Amazon. During this trip she was briefly accompanied by her contemporary Mary Agnes Chase. While in Ecuador, Mexía worked with the Bureau of Plant Industry and Exploration, under the Department of Agriculture. Her work focused on the cinchona or wax palm, and specific herbs that bind to the soil. In personal correspondence from 1980, the botanist John Thomas Howell refers to Mexía as a "close friend of Alice Eastwood." He relates that "In 1933 she accompanied Miss Eastwood and me on the first Eastwood and Howell collecting expedition.….in an open Model T Ford, that traversed parts of Nevada, Utah, Arizona, and California...and netted over 1300 collection numbers... Mrs. Mexía was to me a dear good friend." Nina Floy Bracelin served as Mexía's collection manager In her will, Mexía left sufficient money to the California Academy of Sciences to hire Bracelin as an assistant to Alice Eastwood. All of her research and collecting excursions were funded by the sale of her specimens to institutions and private collectors. Documentation of her expeditions appeared regularly in The Gull, the newsletter of the Audubon Society of the Pacific, from 1926 to 1935. The Sierra Club Bulletin published two accounts of her travels: "Three Thousand Miles up the Amazon" (SCB, 18:1 [1933], 88–96), and "Camping on the Equator" (SCB, 22:1 [1937], 85–91). Several additional were published in Madrono, the journal of the California Botanical Society. Mexía was an active member of many scientific societies, including the California Botanical Society which she joined in 1915, the Sierra Club, the Audubon Association of the Pacific, the Sociedad Geográfica de Lima, and the California Academy of Sciences. She was also an honorary member of the Departamento Forestal, de Caza y Pesca de Mexico. She also guest appeared as a lecturer at various scientific organizations in the San Francisco Bay Area on account of her riveting accounts of her journeys and her skillful photography lending visuals to her content. Her specimens are housed at the California Academy of Sciences (main collection), the Academy of Natural Sciences, Philadelphia, the Field Museum of Natural History, the Gray