From 1994 to 1997 internal research grants from Los Alamos National Laboratory's Laboratory Direct Research and Development (LDRD) office were used to fund an effort aimed at studying global vibration-based damage detection methods. This report summarizes the data that has been collected from the various vibration tests performed on the Alamosa Canyon Bridge, analyses of these data, and the results that have been obtained. Initially, it was the investigators intent to introduce various types of damage into this bridge and study several vibration-based damage detection methods. The feasibility of continuously monitoring such a structure for the onset of damage was also going to be studied. However, the restrictions that the damage must be relatively benign or repairable made it difficult to take the damage identification portion of the study to completion. Subsequently, this study focused on quantifying the variability in identified modal parameters caused by sources other than damage.