A federal agents authority to make arrests for state law violations is a question of state law. In Colorado, the provisions defining peace officer are Colo. Rev. Stat. 16-2.5-101 & 16-3-110. The definition covers law enforcement officers authorized by federal law or employing agency to use deadly physical force in the performance of their duties. In 8 U.S.C. 1357, Congress authorized the Attorney General to issue regulations relating to deadly force. The deadly force regulations are found at 8 CFR 287.8(a)(2). It appears that those federal officers that can use deadly force can arrest a person for a Colorado misdemeanor or felony committed in their presence. The following link includes the authority in all states. http://www.cga.ct.gov/2010/rpt/2010-R-0042.htm
Thanks to Dan Kesselbrenner.