yes there seem to be few trails in the park of any length.
there is the California Hiking and Riding Trail (which several of us ran last spring) but in my view it does not travel thru the most scenic areas.
but in the upper portion there are numerous day hike trails.
I'm very familiar with the upper park but have not spent much time in the lower.
for a first timer who is photography oriented the numerous rock formations of the upper park may be quite interesting. you could camp in one of several camp grounds, or take a short over nighter.
this central, rock laden part is popular with rock climbers and other visitors, but a half mile from the road and you won't see anyone, especially in winter.