Adams Trailhead is a popular place and is usually pretty full in the evenings. I've counted up to 70 vehicles in the parking lot. It's especially crowded on Monday Evenings (Local "Family" night) and Wednesday evenings (Local Boy Scout night).
Adams Trailhead hooks up with a number of trails. After proceeding up the the switchbacks (about a 1/2 mile), if you go left you'll be on Bonneville Shoreline Trail and will reach Kayscreek/Fernwood in about 2 miles. Also at the top of the switchbacks, you'll can see a faint trail right up the side of the mountain that is an unoffical route to Layton Peak.
If you proceed into the canyon, in about a 1/4 mile there is another split in the trail. Across the bridge, to the right will take you to Kaysville Wilderness area (about 1.5 miles) on the Bonneville Shoreline Trail.
If you continue straight into the canyon through the forest for 1.3 miles, you'll reach the waterfall and that is most people's destination.
Adams canyon is located in Layton. The reference to hwy 89 in Kaysville is misleading. Hwy 89 runs through Farmington, Fruit Heights, Kaysville and Layton. The canyon trail head is in Layton, and can be seen at the top of Oak Hills Drive where it meets Hwy 89. The directions that the turn off is west of the water tower are incorrect too. The road is east and north of the water tower on the east side of hwy 89. Adams canyon gets its name from a prominent Layton family and in no way is located in Kaysville.
Thanks for the corrections. I re-wrote the trailhead info. Don't hesitate to contact if you have more info or if I've gotten something else wrong. Appreciate your time.