Spatial and temporal heterogeneity challenges our efforts to interpret current conditions, and to apply appropriate perspective when summarizing in environmental descriptions. We quantified local heterogeneity within a portion of the Área de Conservación Guanacaste (ACG) in northwestern Costa Rica by measuring air temperature, precipitation, and litterfall across numerous sites that were <30 km apart. Annual air temperature averaged 19.5 – 25.9°C across 7 sites. Annual rainfall averaged 1969 – 4240 mm/yr across 10 sites. Rainfall seasonality increased as annual precipitation decreased. These sites are not the wettest or the driest sites in Costa Rica (cf versus >5000 mm/yr or <1500 mm/yr), much less Central America/Caribbean, and not the warmest or coldest sites in Costa Rica either (cf >30°C or <10°C). Annual litterfall averaged 447 – 1083 g AFDM/m2/yr across 10 sites, values well within the range measured for tropical riparian forests, and equal to or greater than observed for temperate riparian forests. Environmental differences among sites in this portion of the ACG reflect a number of factors, including local elevation, topography, and variation in Pacific and Caribbean influences.