Thanks for the forum post, and this research and summary! Very helpful.

As it turns out, some shortcomings in the current system keep this from being a quick fix even for curators (more below). Right now, Establishment Means for relatively widespread species like this one are mostly managed via the Country/State/County hierarchy (or local equivalent). So a little more clarification and detail to your summary above would be helpful. Mainly, for states where not native or introduced throughout, a listing of counties where native, introduced, or unknown/mixture would help.

We can also try to overlap that geographic system with defined places (like San Joaquin Valley, Sonoran Desert, etc.) that have species checklists, but the results of the overlap may be contradictory in some instances. Some of the regions you mentioned above may not have defined geography in iNaturalist, so County equivalents will be all we can use.

Now to the shortcomings (I am brewing up a couple of feature requests to address this):

Currently access to the place-checklists where Establishment Means is maintained is clunky, and so can be pretty time-consuming for widespread taxa (basically taxa present in more than about 100 County-equivalents). One feature request will involve improvements to curator tools via the status tab on the taxon pages.

The other issue is when Establishment Means is "known to be unknown." Information is either contradictory or has been searched for and doesn't exist. We don't currently have a category for that, just a binary Native/Introduced. We can also leave it "blank" which translates to "unknown" in the current system, but that has often been an invitation to make a choice between the binary alternatives. We need a category for when we know a choice is not possible.

Maybe more information than you wanted at present. But for now that refined list by county-equivalent (when not a whole state) would be a good starting place for this taxon.

Well, I went ahead and did the work tonight while things were still in my head. Here's my best SWAG for the county-by-county breakdown:

Note: These designations are in several areas "best guess." Experts with local knowledge will probably disagree with my guesses in many cases. Perhaps we should go with this, and let the community respond. I think my assessment is reliable for the coastal states (WA, OR, CA), but not so good for the interior states.

This is just for the United States. In Canada, BC and Alberta both have this species (and most others) listed as "Unknown" establishment means, and I see no reason to change that without their consent.

Approach: based on the published range descriptions, along with examination of the iNaturalist range map (including GBIF data):

1) Marked as "Native" for any county that overlaps the published range descriptions (see earlier comment).
2) Marked as "Native" any county adjacent to the described range that contains the same biogeographic/floristic units where the species was observed nearby, or has apparently wild observations in suitable habitat.
3) Otherwise, marked as "Unknown," which seems safer than assuming "Introduced" for areas near the known native range.

I'm interpreting "suitable habitat" as open coniferous forest or steppe at low to mid elevations.

Washington: Native for all counties.

Idaho: Few observations, but connecting biogeographic regions suggests Native for all counties except those in the Snake River Plain, so Unknown for: Payette, Owyhee, Twin Falls, Gooding, Lincoln, Blaine, Jerome, Cassia, Bingham, Bonneville, Bear Lake, Jefferson, Madison, Fremont. [NOTE: iNaturalist observations in the SR Plain near Boise and Pocatello appear to be mostly cultivated.]

Montana: Problematic, Published range descriptions include western Montana, but we have only few and scattered observations in the Rocky Mountains. So as a best guess, I'm including all the Rocky Mountain counties as Native: Lincoln, Flathead, Glacier, Sanders, Lake, Mineral, Missoula, Powell, Lewis and Clark, Ravalli, Granite, Deer Lodge, Silver Butte, Jefferson, Broadwater, Beaverhead, Madison, and Gallatin. Other counties (northern Great Plains) can probably remain as Introduced.

Oregon: Native for all counties, except Unknown for Malheur County. (This county fits into the Great Basin exclusion in Intermountain Flora and has little montane confierous forest/steppe that might provide suitable habitat, but has had very patchy botanical exploration.) [NOTE: for Oregon, I also consulted the Oregon Flora Project Atlas (http://www.oregonflora.org/atlas.php) which has records of the species for some counties that lack iNaturalist or GBIF records. This includes records in suitable habitat in Lake and Harney counties, which I had excluded in my earlier comment.]

California: Native for all counties. (Jepson eFlora excluded 3 floristic zones, but none of those zones enclose a whole county, so no counties are excluded.)

Nevada, Arizona, Utah, New Mexico, Wyoming, and Colorado: Unkown. (All these states are within the broadest descriptions of range [Wikipedia], and most have some observations that are in suitable habitat, but disjunct from nearest well-documented native range.)

@jdmore has corrected the coastal states, and I have done so for Idaho and Montana. So, this is completed as far as it is likely to be. The status in the southern Rocky Mountain states has not been resolved, and we made no changes in those states.

I think this flag can be closed, unless somebody wants to tackle the southern Rockies.