This thesis is missing page 123, no other copy of the thesis has this page. -Digitization Centre / This research provides the first detailed study of the coastal geomorphology of Playa Guiones, Guanacaste Province Costa Rica. Playa Guiones is located within a tropical wet/dry climate necessitating that field work is completed in both seasons to ensure a broad understanding of the coastal characteristics. The research commenced February 2005 with site selection and preliminary field work. During June 2005 a detailed real-time kinematic GPS survey and beach inventory (sediment, rock and vegetation) was conducted. During a third field session a comparison was made between the current observed coastal characteristics and those observed during the two other field seasons. Playa Guiones is composed of primarily fine grained sand and carbonate shell material. Rock samples collected adjacent to the southern headland on the rocky shore platform consisted of limestone and finely grained, interbedded sandstone and siltstone. Adjacent to the northern headland on the rocky shore platform the rock consisted of sandstone. Playa Guiones displays some temporal variability which may be linked to the wet and dry seasons. On initial inspection Playa Guiones appears to have the characteristics of an embayed beach but more detailed inspection illustrates that Playa Guiones has many characteristics that are contradictory to a typical embayed beach. Although Playa Guiones lies on a convergent margin it has many characteristics of a divergent margin coast. This study is significant because it provides important baseline information for future work. Playa Guiones is located on the Nicoya Peninsula where a large seismic gap, which last fully ruptured in 1950, is known to exist. The baseline data will be very useful subsequent to any future earthquake event for measuring change that occurs along this rapidly developing coastline. The methodologies employed in this study provide much more detail information than is typically collected in gee-indicator studies which often only measure several profiles along a beach to create a digital elevation model rather than the 3 m gridding distance used in this study. / Thesis / Master of Science (MS)