Depends on how you judge it.
For a dirt motorcyclist/camper, it goes from July 15th when they officially open the forest service roads, until first snow fall which is between Sept 15 and Oct 15 usually.
Two to three months.
But we've had at least a month more spring this year.
If you're asking, "How long is winter and the shitty muddy part of spring before things turn green?" That's usually mid-Oct til mid-may. So, five months of non-winter/shit.
OTOH, it keeps the posers away. You either love nature like life itself, or you don't live here.