Here is the opinion.

An excerpt:

Elon Yallup challenges his conviction for felony driving while under the influence (DUI), arguing that the State cannot enforce the implied consent laws against an enrolled member of the Yakama Nation driving on state highways on the reservation. We conclude that the implied consent statute is primarily a criminal statute rather than a civil regulatory statute as that distinction is applied by the United States Supreme Court in cases interpreting Public Law 280.

Appellant brief is here.

Respondent brief is here.