This data publication contains the results of chemical and mineral analyses on masticated particles from mixed-conifer forests in 15 study locations. These data were collected from 2012 through 2016 as part of the MASTIDON project. The MASTIDON project was a four-year research project to study how masticated material differs when treated with different cutting machines and how the masticated particles decompose when left on the ground for multiple years. It investigated masticated materials in four states of the western United States. The project was funded by the Joint Fire Sciences Program (JFSP) and RMRS between 2013 and 2016. The masticated particles within this project had been decomposing in situ in wet and dry areas of Idaho, Colorado, New Mexico, and South Dakota since their initial treatment. Particles were tested from four shapes (circular, three-sided, four-sided, and small wood chips) and three size classes. Each shape and size class was ground, dried, and analyzed for percent carbon and nitrogen, cellulose and lignin, heat content, and mineral content (from the duff component) using three pieces of equipment. This data publication includes the results of each of these tests and files describing the MASTIDON project and its goals.