Recent structural and geodetic data define the Guatemala City graben region as the continental triple junction between the North American plate, Caribbean plate, and a forearc sliver. We present a minor fault analysis, geochronological and geochemical analyses, and newly updated GPS velocities in western Guatemala, west of the Guatemala City graben, to characterize the magnitude and timing of extensional deformation in this poorly understood area. Elongations estimated from fault data are parallel (~east-west) and perpendicular to the Polochic-Motagua fault system to the north, similar to geodetically-measured active deformation observed east of the Guatemala City graben. Four new ⁴⁰Ar/³⁹Ar dates and correlation of tephra deposits suggests that faulting was active during the Pliocene, but ceased eastward towards the Guatemala City graben over time. From west to east, fault cessation occurred before the deposition of the Los Chocoyos ash (84 ka) and E tephra (51 ka). Faulting just west of the Guatemala City graben appears to be active, where a major fault cuts the most recent Amatitlan tephras. Based on this data, we propose a time-progressive strain model for deformation related to North America-Caribbean plate interactions, whereby distributed elongation of the westernmost Caribbean plate occurred during the Pliocene but localized mostly within the Guatemala City graben and nearby faults during the Quaternary. Our model supports that: 1) The Guatemala City graben is effectively the western limit of the Caribbean plate; and 2) Western Guatemala, which used to be the trailing edge of the Caribbean plate, has been transferred to the forearc region.