sienitic

The geological formation at the site is sienitic gneiss.

Scientific American Supplement, No. 595, May 28, 1887 Various

The general character of the rock here is sienitic; but, besides this peculiar quality of feldspar, the hornblende appears as actinolite, (ray-stone,) so called from the form of its crystallization; while the quartz element is faintly present, or appears in separate masses.

The Atlantic Monthly, Volume 15, No. 87, January, 1865 Various

The summit rock was gneiss, succeeded by sienitic gneiss.

The Life and Adventures of Kit Carson, the Nestor of the Rocky Mountains, from Facts Narrated by Himself de Witt C. Peters

They are generally trap-rock, embracing the varieties of gray, porphyritic, hornblendic, sienitic, and amygdaloidal trap, and appear to have had no labor expended upon them except the chiseling of a groove around the middle for the purpose of attaching a withe to serve as a handle.

Ancient Mining on the Shores of Lake Superior 1865

This is said to be the rockiest shore in Massachusetts, from Nantasket to Scituate, -- hard sienitic rocks, which the waves have laid bare, but have not been able to crumble.

Cape Cod 1865

They are generally trap-rock, embracing the varieties of gray, porphyritic, hornblendic, sienitic, and amygdaloidal trap, and appear to have had no labor expended upon them except the chiseling of a groove around the middle for the purpose of attaching a withe to serve as a handle.

Ancient Mining on the Shores of Lake Superior 1865

The summit rock was gneiss, succeeded by sienitic gneiss.

The Life and Adventures of Kit Carson Peters, DeWitt C 1858

The summit rock was gneiss, succeeded by sienitic gneiss.

The Exploring Expedition to the Rocky Mountains, Oregon and California To which is Added a Description of the Physical Geography of California, with Recent Notices of the Gold Region from the Latest and Most Authentic Sources Brevet Col. J.C. Fremont 1851