44. Riker Hill Park
Riker Hill Park is an excellent location to examine fresh exposures
of sedimentary red beds and basalt typical of the Newark Basin region.
The park is located along the western side of the Newark Basin near Rosedale,
New Jersey, close to the intersection of Interstate 280 with Interstate
287. From Interstate 280 westbound, take Exit 4A and turn south on Eisenhower
Parkway. Drive 1.1 miles and turn left onto Beaufort Avenue. After another
0.4 mile turn left onto the entrance road to Riker Hill Park. Drive up
hill and park at the Geology Museum. Follow the trail from the museum
parking past the ruins of a Nike missile platform, and down hill through
the woods to an abandoned aggregate and building stone quarry in the red
beds of the Early Jurassic Towaco Formation (Figure 101).
|Figure 101. Flaggy sandstone of the Jurassic Towaco Formation at
Riker Park. The high wall at the upper end of the quarry consists
of the Hook Mountain Basalt.
These red bed consist of layered flaggy sandstone and intervening shale
that preserve a variety of very well preserved sedimentary structures
(mostly ripple marks and desiccation cracks) and occasionally trace fossils
(rare dinosaur tracks) (Figure 102). There are numerous small pits where
individuals have pried apart layers in search of tracks. A few tracks
can still be found on some of the larger, immovable blocks of sandstone
that litter the surface. Please don't attempt to remove or modify them!
|Figure 102. Ancient dried lake muds in the Jurassic Towaco Formation
display abundant desiccation cracks and sometimes rare dinosaur tracks
at Riker Park, New Jersey.
The Hook Mountain Basalt stands out as the upper high wall of the quarry
near the top of the hill (see Figure 101). A thin, light-colored chill
zone represents the effect of contact metamorphism in the sedimentary
rock along the base of the lava flow. The basalt displays an abundance
of vesicles, small vertical holes formed from gases venting from the lava
before it cooled. The basalt in the quarry wall also displays poorly-developed
columnar jointing. Some of these vesicles and fractures yield the pale
green zeolite mineral, prehnite.