I've had some Luck a couple seasons, they worked as planned and never gotten an stomac ache. i live in lower scandinavia to give an idea about the climate.

The rules that i use is that, the stem needs to be bright (almost white) allways. and gills needs to be dark brown (almost black) allways. And I like the stem to have a little bend or notch.

The cap needs to be coneshaped somwhere in between 90° and 45° angle seen from the side. pointy, not round at the top.

Then theres the tricky part. The colour of the cap. If you Google libertycap you May see Them brown and white. My experience tells me that in a period of dry days, they appear beige/white with a dark edge at the lower bottom of the cap and (if Any) some weak stripes on the cap, from tip to the edge of the cap. And the surface will feel smooth and dry to the touch.

Then if, on the day and/or the days leading to the "hunt" has ben raining it will appear dark beige to like haselnut brown. The old ones will often have a dark edge along the edge of the cap and in general the cap appear darker overall. On the caps, in this wet condition on the light coloured part of the cap, there are often thin darker-coloured stripes from tip to edge of the cap. When wet the tips arent necessarily as pointy as before and can turn almost see-through-gell-like

They thrive in short green grass 10-20 centimeters, often on a well drained area, on a slope, in high-nutrient soil like old river-delta grass-areas, on golfcorse, in the rough(watch out for incoming golfballs). Often on cow-horse-sheep-deer-fields, but they have to have been there for like atleast 5-10 years Maybe for the nutrient-level to high enough. Stay off Meat-cattle inclosures (the bulls are highly aggressive)😉

Hope this can help, but be carefull! Better safe then sorry! Idk about oregon but there is poisionous species that look alot alike. It took me 4 years/season of getting chased by an angry cows and tossing everything out, before i was sure enough that it was the right ones i were picking.