To cite elevatr:

Hollister J, Shah T, Robitaille A, Beck M, Johnson M (2020). elevatr: Access Elevation Data from Various APIs. R package version 0.3.1, doi:10.5281/zenodo.4282962, https://github.com/usepa/elevatr/.

Corresponding BibTeX entry:

  @Manual{,
    author = {Jeffrey Hollister and Tarak Shah and Alec L. Robitaille
      and Marcus W. Beck and Mike Johnson},
    title = {elevatr: Access Elevation Data from Various APIs},
    year = {2020},
    note = {R package version 0.3.1, doi:10.5281/zenodo.4282962},
    url = {https://github.com/usepa/elevatr/},
  }