Sesqui is the overlooked trail option in Columbia. Harbison is better, but Sesqui has its pluses too.
The official trailhead is inside the state park at the bottom of the hill. I chose to post the option of parking at Polo Road Park instead. The connector trail from Polo Road Park is very close to the loop. If you park inside the state park, the connector to get to the loop is a longer stretch of doubletrack, and lots of it is sandy.
On that note, much of the trail is sandy. During the hot summer, the sand can get pretty deep and loose in places. It makes control a little tough on downhills, and it makes good forward progress tough on uphills. The sections that aren't sandy are typically a compacted bed of pine needles that are good for riding. The entire trail really shines when it's wet. This makes this a perfect alternative to Harbision during these times. While Harbison is muddy, Sequi's sand actually firms up a bit after rain. It makes for good riding when a ride at Harbison would be a mess and harmful to the trail.
The loop is typically ridden clockwise, but it's fun going counter-clockwise too. My GPS measured a single lap at 4.2 miles, but it is a little longer when measured by an accurate cycle computer using the wheel.