www.shroomery.org reports the following:
Amanita muscaria var. guessowii
Region: Eastern/northeastern North America. From northeast Canada, as far south as the Appalachian mountains of North Carolina and Tennessee, and as far west as the great plains (Michigan is the furthest west point where the subspecies has been collected).
Habitat: Mycorrhizal primarily with conifers, but can also occur with some deciduous trees.
Volval material is cream-colored
The cap ranges from orange to yellow-orange, much paler than with typical var. flavivolvata, even in young specimens
This eastern North American species is often mis-named as Amanita muscaria var. formosa, and not without good reason. It is essentially a formosa-like variant of the North American clade of the muscaria group.
DNA studies have not yet shown that all guessowii are descended from a single ancestor, and its possible that the yellow cap is simply a common polymorhism in eastern fly agarics. Therefor it’s possible that the term var. guessowii will become obsolete, and the mushroom will simply be known as the yellow form of Amanita amerimuscaria. If it can be demonstrated that this variety is monophyletic (descends from a single ancestor), then it would likely be renamed to Amanita amerimuscaria var. guessowii.