This data publication contains the results of sorting 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 were created by four different machines, including a vertical rotating head, horizontal drum, chipper, and mower. They had been decomposing in situ in wet and dry areas of Idaho, Colorado, New Mexico, and South Dakota since their initial treatment. Particles were broken down into 15 shape and three size classes. Each shape and size class was counted for total particles and weighed (in grams) for total fuel load by class. The total weights by shape and size class were then aggregated for a total fuel load for the 0.5 x 0.5 sample area at each location and converted to fuel loads for a 1 x 1 meter area. Subsamples of each shape and size class were taken to obtain specific information on the characteristics of particles in each class, such as average length, width, weight, particle density, volume, and surface area. This data publication includes field data on fuel loads, depth measurements, and bulk densities of five fuel layers; lab data from the sorting, characterization, and bulk density measurements of the fuel particles; and files describing the MASTIDON project and its goals.