Manual de Plantas de Costa Rica | The physical environment | 67 
For much more information on Costa Rican geography, including many maps and 
charts, see the superb review in Gémez P. (1986). The overviews of Dodge (1933) and 
Standley (1937b) are also worth reading. 
Geology 
Costa Rica is exceedingly complex geologically, and a comprehensive account is beyond 
the scope of this volume. The following review focuses on exposed formations, and 
other features of obvious or potential influence on the flora. See Weyl (1980), Castillo- 
Mufioz (1983), Gomez P. (1986), Ludington et al. (1987), and Tournon & Alvarado 
(1997) for much more detailed accounts of Costa Rica’s geology, as well as analyses of 
its particularly complicated tectonic history. 
As described in the previous section, Isthmian Central America was built up of 
upper Cretaceous and Tertiary marine sediments and Tertiary volcanics, overlying Ju- 
rassic and Cretaceous rocks of the oceanic crust, with subsequent (Quaternary) vul- 
canism and sedimentation. There are no exposed formations older than lower Jurassic 
in the region, and few if any metamorphic crystalline rocks (Weyl, 1980; Tournon & 
Alvarado, 1997). 
Mesozoic and Paleogene rocks 
Mesozoic rocks are known in Costa Rica principally along the Pacific Coast. The so- 
called Cretaceous basement, an association of alkaline igneous (basaltic) and sedi- 
mentary rocks termed the Nicoya Complex, is exposed in Costa Rica along the north- 
ern Pacific coast, chiefly on the Santa Elena and Nicoya Peninsulas. Basaltic rocks 
similar to those of the Nicoya Complex (and formerly considered part of it) occur 
southward on the Pacific coast: on the Herradura Peninsula, Cerro Turrubares, and vi- 
cinity; at Quepos; and all about the Golfo Dulce region (including the Osa and Burica 
Peninsulas and Isla Violin). These formations are now known to be more recent (upper- 
most Cretaceous and Paleogene) than the Nicoya Complex. Basalts of Paleogene age 
are also known from the Caribbean slope of the Cordillera de Talamanca (Tournon & 
Alvarado, 1997). 
The most conspicuous Cretaceous-age manifestation of plutonism in Costa Rica is 
the Santa Elena Peninsula. This unit is, for the most part, a massif of serpentinized peri- 
dotite (Azema & Tournon, 1980; Tournon, 1994), derived from the upper mantle and 
described by Wey] (1980: 143) as “something of a foreign body in the structure of Costa 
Rica.” That this body may extend to the Caribbean slope, 150 km eastward, is suggested 
by the recent discovery of peridotite-serpentinite rocks similar in age, texture, and min- 
eral chemistry to those of the Santa Elena Peninsula on both the Nicaraguan and Costa 
Rican sides of the Rio San Juan (see Tournon et al., 1995). In addition to their obvious 
