A Californian sidewalk delta-8 vendor was recently arrested [3] in Ocean Beach for selling unlicensed delta-8 products. The SDPD confiscated his inventory and cited him for possession of cannabis for sale. 

You cannot cross California state borders with delta-8 THC products [4] unless they carry below 0.3% THC. The state restricts and regulates all unlicensed delta-8 products above the 0.3% combined THC concentration.
Likewise, you cannot enter California with marijuana-derived delta-8, even though the state legalizes medical and recreational cannabis. 
The federal government controls all state borders and considers marijuana illegal. Entering California with marijuana could be seen as drug trafficking, a felony crime.