Glen Avon Quarry (Glen Avon Limestone deposit; Mathews), Glen Avon, Riverside County, California, USAi

Regional Level Types
Glen Avon Quarry (Glen Avon Limestone deposit; Mathews)	Quarry
Glen Avon	- not defined -
Riverside County	County
California	State
USA	Country

The Glen Avon “quarry” consists of 3 small excavations near the top of a hill, NW of the coordinates shown as you suggest (same as Mindat coordinates- Steve Stuart). It was originally operated as a source of grit for chickens. (They need calcite to produce good egg shells.) It has been abandoned for at least 70 years (Robert Housley).

Following our meeting in August, 2001 Anne Seminaris led a field trip to the nearby Glen Avon Quarries. Even though it was an uncommonly hot day about ten people participated. Fortunately we found a route that allowed us to drive almost to the first small quarry of the three. I had been here many years ago on an MSSC field trip led by Mel Larsen and so remembered a little about what to expect. These small quarries have not been worked in a long time and everything is overgrown and dirty. At first they do not appear promising, but in fact they are pretty interesting.

The first and southernmost quarry, also the smallest, is totally in recrystallized limestone. In the coarser parts where the calcite rhombs get up to about an inch across there are regions containing nice micros of golden brown phlogopite. In the finer grained dark appearing calcite there are regions with nice graphite micros. A couple of small regions near the entrance on the right contain fine grained purple spinel and chondrodite. I found one axinite crystal in weathered material on the left. A pit below this quarry contains veins of fibrous tremolite.

The walls of the two larger quarries are largely calc-silicate rock and I spent the bulk of my time with that. Below the middle quarry I broke up a rock that contained numerous cinnamon brown garnets to about half and inch, but mostly smaller.

In the northern quarry I worked and area of the north wall that appeared to be a very dirty porous plagioclase and brought home several chunks. They required a lot of cleaning and trimming, but proved to be quite interesting. It appears that at one time this rock was an intergrowth of diopside and plagioclase with minor titanite and zircon. It appears that as the temperature dropped in the fluid rich environment diopside became unstable and was largely leached out. Later still actinolite, axinite, and apatite were deposited in the resulting cavities. After much cleaning I recovered nice micros of all the minerals mentioned from these pieces. The axinites are especially well developed.

Even though we worked in slow motion because of the heat I think everybody found something of interest. About 5:30 though we all decided we had had all the fun we could stand for one day and retired to a nearby Mexican restaurant recommended by Anne for food and refreshment and conversation. Now I am ready to go back to Glen Avon and try it again soon.