An attractive watercolour and ink manuscript map which has to be one of the earliest to detail the mouth of the Colorado River. At the time the mouth fed one of the largest desert wetlands in the world with over 2 million acres being supported. The Dams along the river today have cut off that supply entirely changing the landscape considerably. The map extends eastwards to the Rio Ascunsion, north to the present day Arizona border and includes the Bahia Adair and Bahia S. Jorge. Near to the mouth of the Colorado the lowlands are labeled Marismos and Medanos de Arena. The local Yumas Indians are noted also with a number of villages noted particularly to the west of the River. With ‘Ex Libris Dei Marques de Pidal no. 56’ on the verso. Pidal (1846-1913) was an active book collector, politician and philanthropist whose collection remained with the family until the early 1960s.