Paul and I did a clockwise loop with a few miles off-trail, see the caltopo route below. We saw 54 species of plants in flower, Paul's list is below, thanks Paul! On the upper flats there were thick areas of gold stars, sagebrush violets, and rock onions. The bluff above the northern entrance to the canyon has some thick displays of balsamroot and lupine (photo 1). The bootpath down from that bluff is steep and a little treacherous (even with poles).

FLOWERING PLANTS IN BLOOM (49 species)

white (13 species)

western serviceberry (Amelanchier alnifolia)
annual Jacob’s-ladder (Polemonium micranthum)
wax currant (Ribes cereum)
panicled death-camas (Toxicoscordion paniculatum)
sagebrush stickseed (Hackelia diffusa)
longhorn plectritis (Plectritis macrocera)
spring whitlow-grass (Draba verna)
chickweed, species uncertain (Cerastium sp.)
big-seed desert-parsley / biscuit-root (Lomatium macrocarpum)
Gorman’s desert-parsley / biscuit-root (Lomatium gormanii)
milk-vetch, probably Yakima (Astralagus, probably reventiformis)
cushion pussytoes (Antennaria dimorpha)

rock onion (Allium macrum)

yellow (14 species)
holly-leaf Oregon-grape (Mahonia / Berberis aquifolium)
golden currant (Ribes aureum)
nine-leaf / triternate desert-parsley / biscuit-root (Lomatium triternatum)
Umtanum desert-parsley / biscuit-root (Lomatium quintuplex)
Carey’s balsamroot (Balsamorhiza careyana)
Hooker’s balsamroot (Balsamorhiza hookeri)

hybrid Hooker’s x Carey’s balsamroot (Balsamorhiza hookeri x careyana)
arrowleaf balsamroot (Balsamorhiza sagittata)
false agoseris / desert dandelion (Nothocalais troximoides)
desert spring gold (Crocidium multicaule)

Columbian puccoon (Lithospermum ruderale)

desert yellow daisy (Erigeron linearis)

arrow-leaf buckwheat (Eriogonum compositum)

field mustard (Brassica rapa)

bluish: blue to violet to blue-purple (7 species)

ball-head waterleaf (Hydrophyllum capitatum)

lupine, maybe silky (Lupinus, maybe sericeus)

rock lupine (Lupinus saxosus)

large-flower triteleia (Triteleia grandiflora)

sagebrush violet (Viola trinervata)

upland / common larkspur (Delphinium nuttallianum)

small-flowered blue-eyed Mary (Collinsia parviflora)

reddish: pink to red to red-purple (12 species)

red-stem / common stork’s bill (Erodium cicutarium)

blue mustard (Chorispora tenella)

bulbous prairie-star (Lithophragma glabrum)

apple tree, species uncertain (Malus sp.)

showy phlox (Phlox speciosa)

midget / fragile phlox (Microsteris gracilis)

tufted phlox (Phlox caespitosa)

rockcress, probably Columbia / few-flowered (Boechera, probably pauciflora)

dagger-pod (Phoenicaulis cheiranthoides)

thyme-leaf buckwheat (Eriogonum thymoides)

big-head clover (Trifolium macrocephalum)
shooting-star, pretty or desert (Primula pauciflora or conjugens)

orange (1 species)
fiddleneck, species uncertain (Amsinckia sp.)

brown (1 species)
chocolate-tips (Lomatium dissectum)

green (1 species)

Rocky Mountain / Douglas’s maple (Acer glabrum)

BIRDS
Black-capped Chickadee
Spotted Towhee
White-crowned Sparrow
European Starling
American Goldfinch
Canyon Wren
Violet-green Swallow
House Finch
Song Sparrow
Turkey Vulture
Steller’s Jay
Northern Flicker
Common Raven
Western Meadowlark
Horned Lark
American Kestrel
California Quail
Chukar
Yellow-rumped Warbler

BUTTERFLIES

Cabbage White (Pieris brassicae) — many

?Sagebrush Checkerspot (Chlosyne acastus)

Julia’s Orange-tip (Anthocharis julia) — several

Anise Swallowtail (Papilio zelicaon) — several
Sheridan’s Green Hairstreak (Callophrys sheridanii)

MAMMALS

Yellow-bellied Marmot (Marmota flaviventer)

Mule Deer (Odocoileus hemionus) — three groups, of 4, of about a dozen, and of 2

REPTILES

Gopher Snake (Pituophis catenifer)

Western Rattlesnake (Crotalus oreganus)

We had camped 2 nights at Big Pines CG and winds were so strong in the evening we were not able to have a campfire. On our way home today, we stopped at the Umtanum Creek Canyon TH to walk the first mile of the trail to the first creek crossing.  The winds followed us and were present along the trail with frequent higher gusts! There were not many flowers yet, but the golden current, wax current and Oregon Grape added color to the area. One purple fern-leafed desert parsley and 2 balsamroot plants were seen. Our "Picture This" App said the blossoms on a tree were plum blossoms. This tree was seen near the first creek crossing. The apple tree seen shortly after the first creek crossing had buds but no blossoms.

Rode my bike in from the north end of the Yakima Canyon to the Umtanum recreation area. Wide shoulders for 95% of the road, I was pleased with the general safety levels. This trail technically allows bikes, but there' a sign specifically asking for no e-bikes. Very quiet after crossing the bridge - I saw only 2 groups through the entire evening and morning.

The entirety of the trail is on BLM land, making for a perfect early-season backpacking trip. I set up camp about 0.5 miles in at the first "established" dispersed site with a fire pit. The creek is running really high, I didn't cross at the crossing about a mile in. Still a beautiful trail that's lush with life. Wildflowers are beginning to pop and will probably be lining the canyon in a couple weeks.

It’s a sweet little hike up what is typically a small meandering creek. Water levels so high though that at the first crossing, about a mile in, we had to turn around. I’d go back in a month and try again..  

I saw Mytho-man’s photos a few days ago and knew I had to check out this trail.
The hiker guide needs to be updated regarding the required parking pass. You either need an America the Beautiful pass/Golden Age pass or pay the day fee for a BLM pass which you can do on site. Discover Pass won’t do it. Vault toilets are clean and well stocked.
Crossing the Yakima River suspension bridge is a good way to start the hike. Lots of fishermen in the river. We referred to the WTA guide a number of times which helped us stay on track. Sometimes, what looks like the main trail, is not the right way to go. The first creek crossing was easy. My husband crossed on a log and I had more confidence in my waterproof boots so I just stepped across on a wet rock. We both stayed dry.
This trail is so easy to walk on it’s hard to believe there is any elevation change at all. There are times when the plants encroach on the trail but nothing difficult. The second creek crossing had a number of trees to cross on. They looked like they suffered fire and beaver damage. I saw a little fish here. Eventually we came to a point where a tree blocked the trail and the plants seemed to take over. Maybe 2.5 miles in. We decided to turn around and find a lunch spot.
We saw a number of deer high up on the ridge and saw scat from coyotes, mice, deer, elk and bighorn sheep.
Wow, what a great trail. Clean and peaceful. Not a single piece of trash. It sounds like there is a shooting range somewhere out there. While we ate our lunch, the silence was broken by gunshots far in the distance.