The A Loop a pleasant, moderately-difficult hiking and biking trail with lots of switchbacks and some nice elevation changes, plus some very pretty views of the Tyler State Park forest.
You can park at the Blackjack camping area then walk back up the road just a little bit to get onto the trailhead.
I’m sorry to say that I tend to forget about A Loop (my favorite trails are the more-challenging C and D Loops at the opposite side of the park) but I enjoyed it so much during my last walk that I’m going to work it into my regular hiking rotation from now on.
All the hiking/biking loops are connected so you could, if you wanted, hike for over 9 miles without interruptions!
A Loop is listed in the official Tyler State Park Trail map as being 2.53 miles long and taking 1.5 hours to complete, although it was closer to 1.25 hours for me (including time to stop and take photos.)
In the photos below I started at the shared EZ Loop/A Loop trailhead and went clockwise.