The El Dorado Adventure — Lloyd Alexander

Vesper Holly is surprised as her guardian, Brinnie, when she receives a mysterious summons to Central America signed by Alain de Rochefort. Vesper sets sail at once to find de Rochefort and explore the land that she has inherited. On her arrival she makes a terrible discovery--de Rochefort represents the evil Dr. Helvitius, who plans to build a canal on Vesper's land, uprooting the native Chirica Indians for pure profit! Can Vesper overcome the dangers of earthquakes, volcanoes, and the evil doctor in time to save her Indian friends?