While walking around the area, I came across a monument dedicated to Chinese immigrants. It is near the site of where the first Chinatown in Riverside was formed. Not much remains of the original townsite, but there is a small memorial here that has some interesting geology!
The memorial incorporates several basalt columns, known as columnar basalt. It forms when lava flows cools. The cooling (from top to bottom) causes the rock to fracture (or joint). The rock fractures at intervals of approximately 120 degrees as the contraction stress is most easily relieved in this orientation. This is why columnar basalt tends to have a hexagonal shape when viewed from the top, although, in theroey, they can have other shapes as well.
The fracture then propagates very slolwy downward as the lava cools and hardens, forming hexagonal columns (although columnar basalt has been known to have anywhere from 3 to 7 sides, depending on the compositon of the basalt and its cooling rate. A high number of sides suggest that the basalt cooled rapidly, while a low number suggests they cooled very slowly.
Works Cited
https://www.nps.gov/subjects/volcanoes/columnar-jointing.htm
https://www.geologyin.com/2015/10/mystery-solved-how-these-rocks-got.html
TO LOG A FIND ON THIS CACHE YOU MUST ANSWER ALL OF THE QUESTIONS BELOW. You can contact me through the geocaching message center or email to submit your answers. Any incorrect answers may result in a clarification response.
Note: You will only receive an email from me if I need clarification on your answers. You are free to log the cache as a find whenever you like.
1. "Chinatown Basalt" on the first line of your message AND list all geocaching names of your party so I can match your answers to them. If you all want to learn something, I would prefer each cacher send me individual emails in the spirit of earthcaching.
2. Take a photo of your favorite basalt column using some sort of scale. Geologists often use coins, GPS', pens, shoes, notebooks, ect. You might want to be creative in what you use for your scale, however, the scale that you choose is entirely up to you. Make sure your photo is close enough to capture the mineral grains which should be clearly seen! This photo MUST be attached to your "found it" log at the time of when you submit your log. Please do not send any photos through the message center as Groundspeak compresses images. Each log MUST have a unique and different photo. No two logs may contain the same photo.
3. Describe the columnar basalt by telling me their (a) range of colors, (b) textures, (c) average heights, and (d) average widths.
4. On average, how many sides (or faces) do these columns have? Are they truly hexagonal or are they a different shape? Explain.
5. Based on your answer to number 5, how would you describe the cooling rate of the basalt? Was it fast or slow?