Californium isotopes of mass numbers 249, 250, 251, and 252 have been identified by mass spectrometric analyses of californium samples produced from neutron-irradiated plutonium. The half-lives of Bk249, Cf249, Cf250, Cf252, and Cf253 are 290+/-20 days, 470+/-100 years, 10.0+/-2.4 years, 2.2+/-0.2 years, and 18+/-3 days, respectively. The alpha-particle energies of the most prominent alpha peaks for Cf249, Cf250, and Cf252 are 5.81+/-0.03, 6.033+/-0.010, and 6.117+/-0.010 Mev, respectively. The plot of alpha-particle energies vs mass number for the isotopes of californium shows a break (i.e., the alpha energy of Cf252 is larger than the alpha energy of Cf250) indicating an irregularity in the nuclear energy surface. The alpha spectra of Cf250 and Cf252 exhibit characteristic even-even nuclide fine structure peaks. The beta-particle energy of Bk249 is 80+/-20 kev. The spontaneous fission half-lives of Cf250 and Cf252 are 1.5+/-0.5×104 and 66+/-10 years, respectively. Lower limits of 2×108 and 5×106 years have been placed on the partial spontaneous fission half-lives of Bk249 and Cf249. The pile (Materials Testing Reactor at Arco, Idaho) neutron capture cross sections of Bk249, Cf250, Cf251, and Cf252 are 350, 1500, 3000, and 25 barns, respectively.