Huh, interesting. One of our cats just had radiation treatment for hyperthyroidism, and they specifically told us we have to flush the waste (with scoopable, flushable litter) because if we dispose of it in the trash like we usually do, the radiation levels might set off detectors at the waste management facility. So I don’t think it’s illegal in all of California (we’re in the Bay Area, and I’ve never heard this.)