(Montana, Idaho, Wyoming, Nevada, Utah, Colorado)

In the Mountain region, trees usually pollinate from March to May. The primary allergy-causing trees include the cedar, maple and oak. Other trees that may trigger allergies are the box elder, alder, birch, juniper and ash.

Grasses pollinate from April to July in this region. Some of the more problematic grasses include quack grass/wheat grass, redtop, brome, Bermuda grass and orchard grass.

Weeds take over from early June through October, including ragweed, tumbleweed and chenopod. Other weeds that may cause allergies include waterhemp, pigweed, iodine bush, saltbush/scale, sugarbeet, lamb's-quarter, Mexican fire bush and Russian thistle.