Coppertone and I went to the park today and hiked about 5 miles, but barely a foot on the park's official trails. Instead, we hiked the peninsula leading to what is typically known as Sometimes Island. The recent drought have exposed a large spit of land that used to be under the lake. Water levels now are low enough that there's a continuous land bridge from the park.
We spend a few hours looking at shells, the foundations of the old tramway that was used to construct Mansfield Dam and logging a couple of caches.
There's not a trail on the peninsula, but there's relatively sparse vegetation that's taken root, even with the extended drought, so there's little or no resistance to meandering in any direction that you want.
When the spring rains come (hopefully) the land bridge will resubmerge and your opportunity to explore this spot will disappear with it.