@DwightET How exciting! As @hikermor already stated, the Grand Canyon often has snow in December (I normally live in Arizona, so I can attest to this). I would recommend a slightly more southern route, closer to Tucson, AZ. Mount Lemmon, located just outside of Tucson, is surrounded by the Coronado National Forest and offers outdoor activities year-round (summit activities in the summer, lower mountain activities in the winter). The wilderness area offers a scenic drive for site-seers, a vast network of hiking/backpacking trails (including part of the AZ Trail!), hundreds of crags for climbers, many free established campsites (as well as free camping on the national forest land), as well as many mountain-biking paths. In this area you will also find the Arizona-Sonora Desert Museum and Saguaro National Park. Although the nights get a bit chilly, Mt. Lemmon's lower mountain and the general Tucson area (including the museum and National Park) offer wonderful temperatures for winter adventures (and no snow! - Although you can see the snow that we often get on the upper mountain close to Mt. Lemmon's summit!). If this area interests you, I can tell you more about where to stay / what to do, depending on what you're looking for.
Eastern New Mexico also has White Sands National Monument, which is a beautiful place to visit, although I am not sure about their operating hours/weather conditions in the winter.
one or more gifts or other benefits from the co-op.