Previous work demonstrated that Ixodes spinipalpis ticks maintained an enzootic cycle of Borrelia bissettii and the agent of human granulocytic ehrlichiosis (aoHGE) within woodrats (Neotoma mexicana) and deer mice (Peromyscus maniculatus) in northern Colorado (USA). Because I. spinipalpis is the only known vector of B. bissettii and aoHGE in Colorado, this study was designed to determine the reservoir status of other hosts of I. spinipalpis in five distinct ecological zones along the front range and foothills of Colorado. One hundred and twelve rodents of nine species were examined and 11 (10%) were polymerase chain reaction (PCR) positive for aoHGE; 37 (33%) were culture positive for B. bissettii, and five (4%) were coinfected with both organisms based on PCR and culture. Of these, three chipmunk species (Tamias minimus, T. quadrivittatus, and T. umbrinus) were culture positive for B. bissettii, with a single T. minimus coinfected with B. bissettii and aoHGE. In addition, one golden-mantled ground squirrel (Spermophilus lateralis) was positive for both B. bissettii and aoHGE. This is the first report of a golden-mantled ground squirrel harboring either B. bissettii or aoHGE and the initial observation that chipmunks may be a reservoir for B. bissettii in Colorado.