Answer:
the main ridge line of the cascades forms several continuous county borders in Oregon
running from south to north
between Douglas lane linn Marion clackamas & multnomah counties to its west
&
klamath deschutes Jefferson wasco & hood river counties to its east
&
after a gap
the same ridge line also forms several continuous county borders in Washington
running again from south to north
between Lewis pierce king snohomish skagit & whatcom counties to its west
&
yakima kittitas chelan & okanogan counties to its east
so it alone borders 21 counties in all
& in fact forms no fewer than 18 of their mutual borders
& that total accounts only for the main ridge line & the most important geopolitical borders upon it
in addition there are many other ridges of the cascades
which form many less important boundaries as well