To cite package 'extRemes' in publications use:

Gilleland, E. and R. W. Katz, 2011: New software to analyze how extremes change over time. Eos, 92(2), 13--14

Corresponding BibTeX entry:

  @Article{,
    title = {New software to analyze how extremes change over time},
    author = {Eric Gilleland and Richard W. Katz},
    journal = {Eos},
    year = {2011},
    volume = {92},
    number = {2},
    pages = {13--14},
  }