Minis made for the Canadian market in the 70s had emissions equipment to meet North American emission standards. I do not know if California standards were met. AFAIK no other Mini was so equipped. So unless your Mini is a Canadian one you are unlikely to find what you are looking for.  

Minis were never manufactured in Canada. All ours came from the UK. I did own a Mk1 Countryman registered as a 1968, no smog pump on an 848, and then a Mk2 Saloon registered as a 1969. It had the smog pump on a 998.

someone else here may be able to help you on 1971 Mini specifics, whether they had any emissions equipment, and how to prove it to California DMV.  I don't know of any MK1s manufactured after 1970, and that was in Australia, not Canada.  MK1 production in the UK ended in 1967.

https://www.dmv.ca.gov/portal/vehicle-registration/new-registration/register-an-imported-vehicle/  

• "Additional evidence: A copy of a letter from the manufacturer confirming that the vehicle meets FMVSS and U.S. emissions standards.

Usually you can only get this evidence for vehicles manufactured in Canada.

• A copy of the Department of Transportation bond release letter from the National Highway Traffic Safety Administration (NHTSA).
• A certificate stating that the vehicle has been inspected by a California Air Resources Board-licensed laboratory.
• Evidence that the vehicle meets Environmental Protection Agency (EPA) and California emissions standards.
  • This includes an EPA and California emissions label attached to the vehicle.
  • A smog certificate.
  • This applies to gasoline vehicles manufactured after 1968.
  • This also applies to diesel-powered vehicles manufactured after 1980."
  •  

Homework first !

I suspect you're going to be in trouble, and unable to register the car in California.

DMV (California) just asked me for a US Emissions i order to register my just imported to US 1971 MK1 998 mini. Someone who can help me pls.