The California HIgh school Cosmic ray ObServatory (CHICOS) is a collaborative project involving Caltech and Los Angeles schools to field a large array of particle detectors in Southern California. The detectors are located on school rooftops, and utilize the power and network infrastructure available at the schools. The project offers unique educational opportunities for teachers and students at the participating schools. The main scientific goal is to study cosmic rays at ultra-high energies E>10¹⁹ eV. We have installed a total of 65 sites so far, and are collecting data as we continue to
deploy additional sites. We already have a small sample of large air showers and we have studied our system with a smaller array on the Caltech campus.