Key Feature:
FANGLOMERATES are sedimentary rocks. They contain shattered angular clasts (rocks) because of heavy frosts and deep snows eroding down steep slopes as alluvial fans. In comparison, conglomerates contain clasts that are usually more rounded as they are eroded and deposited by fast-flowing rivers, or by waves on beaches. 
Background:
We acknowledge the Ngunnawal people as traditional custodians of this region. This EarthCache is located at the Australian National Botanic Gardens. Note the 'The Aboriginal Plant Use Trail' in the gardens nearby.
The gardens, established in 1949, are located at the foothills of Black Mountain. It is therefore not surprising that fanglomerates can be found in this area at the base of the steep mountain slopes.
Geology:
Over the past two to three million years global climate has fluctuated between periods known as GLACIALS (approximately 20,000 years ago) and INTERGLACIALS (present-day climate). In our immediate region some of the evidence comes from examining preserved fossil pollen trapped in sediments beneath the floor of Lake George NSW north/east of the ACT.
It is thought that in the Canberra region Glacial Periods were colder and drier than at present with the landscape dominated by sub-alpine grasslands rather than Eucalyptus woodlands. This is believed to have resulted in significantly greater erosion and the accumulation of frost-shattered aprons of rocky sediment on the lower slopes of the surrounding hills and mountains. The best known exposed fanglomerates in the region are around Black Mountain, and in the 'Rainforest Gully' of the Australian National Botanic Gardens.
The fanglomerate at the Gardens show that the clasts are only partially worn and are more angular than those clasts found to have been in running water. While the exposed fanglomerate at 'Virtual Stage 01' looks fragile and ready to collapse it is however one rock. The clasts that are visible are typically cemented by calcium carbonate, iron oxides, silica and/or hardened clay into a firm rock.
Fanglomerate: with varied angular sized clasts, Australian National Botanic Gardens. Photograph taken: July 2022.
Access:
The Australian National Botanic Gardens is open every day from 8:30am to 5:00pm except Christmas Day. It is free to enter the gardens although there are parking fees. Access to the rainforest boardwalk is via steep stairs down.
Logging Requirements:
To log this cache you will need to address the following 4 points (questions and mandatory photo). Send your answers via 'Message Center' to the CO as the preferred method. You can log this cache with the required photo immediately. If there are issues with your answers or photo you will be notified.
Questions / Photos:
Virtual Stage 01: Rainforest Gully Boardwalk:
Facing south, there are two distinct areas of exposed fanglomerate rock-cuttings in front and above you.
1. In what geologic period was this fanglomerate formed, and what is its approximate age?
2. What are the approximate sizes (in centimetres) of the biggest and smallest clasts that you can see in either section?
3. Explain why all the 'loose rocks' in the rock-cuttings are not tumbling down onto the boardwalk below?
4. Can you see any uniformity between the clasts (yes/no), and what is the reason for your answer?
5. Post a photo of yourself, or something that identifies you with the greenery and/or boardwalk as the background.
Consider posting additional photos that would encourage others to visit these beautiful gardens.