To cite package 'extRemes' in publications use:

To cite extRemes in publications use:

  Eric Gilleland, Richard W. Katz (2016). extRemes 2.0: An Extreme
  Value Analysis Package in R. Journal of Statistical Software, 72(8),
  1-39. doi:10.18637/jss.v072.i08

A BibTeX entry for LaTeX users is

  @Article{,
    title = {{extRemes} 2.0: An Extreme Value Analysis Package in {R}},
    author = {Eric Gilleland and Richard W. Katz},
    journal = {Journal of Statistical Software},
    year = {2016},
    volume = {72},
    number = {8},
    pages = {1--39},
    doi = {10.18637/jss.v072.i08},
  }