This Cortinarius is a reliable indicator of the end of the mushroom season. In this area the end of June or beginning of July ushers in the mushrooms. By the end of August, the season has begun to taper off and usually little remains by late September. However, it is about this time, late September to very early October, that Cortinarius populina appears. It invariably occurs where there are cottonwoods (Populus augustifolia, P. wislizenii, and P. XASEMMINATO [sic] ), and it fruits in profusion. Single specimens, small to large clusters, or great fleshy heaps appear on bare soil, leafy debris, or even through thick sand in arroyos. Its general appearance is rusty brown, although there may be a faint 0 over the caps as it breaks through the soil or leaves and the entire fruiting body assumes this rusty appearance as well.
    Clearly a Phlegmacium, the stipe is thickened below, the cap is innately fibrillose, the gills pallid fleshy color to faintly brownish at first and the veil copious, membranous, and loose becoming little more that a pale cottony remnant on the stipe. The fruiting bodies are generally medium sized, fairly tall in stature and somewhat irregular in shape.
    Due to the lateness in fruiting the ground has often become dry so that the sporocarps break through hard packed dirt and become somewhat distorted. Also due to the tendency for our fall period to be dry, the fruiting bodies often dry in place and become mummified so that much later in the fall (November, December) one can encounter large clusters of completely dried Cortinarii remaining in place just as they emerged from the soil much earlier in the season.
    There is something poignant about finding this last of the season Cortinarius in one's walks—a sort of requiem for the past year's mushroom season and conveying the knowledge that it will be a full season ahead before any mushrooms will be again festooning our landscapes.