The transition from sand ripples to megaripples encodes information about the physics of how both sand-sized (moved via saltation) and coarsegrained (moved via impact creep) particles interact under Martian conditions. Previous studies have focused on the aeolian mobility of sand on Mars; here we examine how mobile sand interacts with larger particles moved by creep. HiRISE images of small dunes (lacking well developed slip faces) on Mars reveal a transition of aeolian bedform scale with increasing distance from the dune. Here we document the particles in a similar transition on Earth. High Resolution Imaging Science Experiment (HiRISE) images have documented that sand is moving at many locations around Mars under current conditions. Unlike the active sand deposits, enigmatic “Transverse Aeolian Ridges” (TARs; the non-genetic term for linear to curvilinear aeolian bedforms resulting from either dune- or ripple-forming processes) are found at locations widely distributed across Mars. Recently bright TARs were documented to have moved in HiRISE images taken many Earth years apart at three widely separated locations. Great Sand Dunes National Park and Preserve (GSDNPP) in Colorado has a bimodal particle size distribution along with a seasonal bimodal wind regime, providing the setting to examine the transition from sand ripples (<1 cm in height) to megaripples (typically ~25 cm in height). A Smithsonian Scholarly Studies Award for FY19 funded trips to GSDNPP during May and September of 2019 to collect thousands of digital photographs of ripple-megaripple transitions that were later processed using Multiview Stereo Photogrammetry software to produce detailed Digital Terrain Models (DTMs). The digital images were obtained using a Nikon camera that was motor-driven along a track above the study area. The track was then manually advanced following each photo traverse. Photos were obtained using both a 35 mm lens and a 85 mm Macro lens. The DTMs clearly resolve individual coarse (1-2-mm diameter) particles on the bedforms, providing a detailed record of the surface distribution of coarse grains across both sand ripple and megaripple bedforms, including cases where the crests were continuous between sand ripples and megaripples.