Why can't the counties that support the proposed state of Jefferson appeal directly to the federal government for statehood? California and Oregon will never say yes despite nearly all the counties supporting the split, so what options do they have?
Article IV, Section 3, Clause 1 of the US Constitution:
New States may be admitted by the Congress into this Union; but no new States shall be formed or erected within the Jurisdiction of any other State; nor any State be formed by the Junction of two or more States, or parts of States, without the Consent of the Legislatures of the States concerned as well as of the Congress.
Any division of territory from previous states probably isn't going to work out barring something extraordinary like WV during the Civil War.