Family Level ID: Ventral abdominal gills, forked anal prolegs with fans.
Genus Level ID: Large prosternal sclerites present (Figure 2), pair of sclerites present on abdominal segments 8 and 9 (Figure 4), forked foretrochantin present (Figure 5), frontoclypeus is not notched (Figure 7), submentum notched (Figures 8 and 9).

Family ID: Based on long antenna, simple gills.
Genus ID: third caudal filament is reduced to a singular nub, long hairs coating femur, tibia and tarsus.

The only species of Acentrella within Colorado/within the South Platte drainage basin are A. insignificans, A. turbida, and A. parvula. I suspect this is A. insignificans based on the presence of hind wingpads (A. turbida does not have hind wingpads). A. parvula is critically imperiled within Colorado so this is likely not that species.

Family ID: "long" antenna (visible in Figure 2)

I suspect that this is Oecetis, as the maxillary palpi do look pretty long and the mandibles are pretty long and blade-like (Figure 4). The only other genera of Leptoceridae found in Colorado include Triaenodes/Ylodes and maybe Ceraclea.

Family ID: Ventral abdominal gills, forked "fans" on anal prolegs, 3 dorsal sclerites on nota
Genus ID: Forked foretrochantins (Figure 8), posterior margin of each sclerite on abdominal sternum IX notched (Figure 3, very faint/indistinct though), small pair of sclerites found under prosternal plate (Figure 2)

Family ID: Head & body dorsolaterally flattened, margins of head visible beside the eyes.
Genus ID: Edges of maxillary palps stick out at the sides of the head (Figure 1), fibrilliform portion of abdominal gills 2-6 absent.
I'll probably try to practice mouthpart dissection on this guy at some point

Family ID: Short cerci, glossae shorter than paraglossae.

I suspect this is Sweltsa due to the darking clothing hairs on the thoracic sterna, lack of vertical intrasegmental hairs on the cerci, and setae on the posterior + anterior margins of the pronotum

Family ID: Based on abdominal prolegs with tiny hooks (Figure 6) present along with short segmented legs on thorax (Figure 5).
Genus ID: Prominent mandibles visible (most visible in Figures 4 and 5). Thorax and abdomen have filamentous gills.