The Tenth Circuit determined that some conduct under section 211 of the California Penal Code (robbery) matched the generic definition of extortion, while other conduct matched the generic definition of robbery. Though the conduct criminalized under the robbery statute matched one generic definition of a crime of violence, as defined in the sentencing guidelines, the court still concluded that a conviction for robbery in California would qualify as a crime of violence under the sentencing guidelines.
The Tenth Circuit's decision potentially creates a split with the Ninth Circuit, which determined in United States v. Dixon that a robbery conviction would not qualify as a violent felony under the Armed Career Criminal Act (ACCA). The Ninth Circuit also acknowledged that some conduct under section 211 of the California Penal Code, and some would fall under the "use of force" definition included the in ACCA. Notably, the ACCA definition of a violent felony does not include a generic robbery definition, nor did the Ninth Circuit discuss whether all conduct criminalized under section 211 of the California Penal Code would fall under either the generic extortion or the use of force definition of a violent felony. Thus, the Tenth Circuit and Ninth Circuit case law may, in the end, be reconcilable. However, this is an area to keep an eye on further developments.
The full text of the Tenth Circuit's decision in United States v. Castillo can be found here: https://www.ca10.uscourts.gov/opinions/14/14-4129.pdf
My blog post on the Ninth Circuit's decision in United States v. Dixon can be found here: http://www.sabrinadamast.com/journal/2015/11/22/ninth-circuit-holds-that-california-robbery-is-not-a-violent-felony-under-the-acca