Skip to content

Golden Beam! JinmianShan EarthCache

Hidden : 07/27/2020
2.5 out of 5
3 out of 5

Size: Size:   other (other)

Join now to view geocache location details. It's free!


How Geocaching Works

Please note Use of services is subject to the terms and conditions in our disclaimer.

Geocache Description:

The uniqueness of Jinmianshan

Jinmianshan is located at Neihu, Taipei. From the hiking route in the picture below, the landscape of the mountain can be discovered. The uniqueness of the mountain is that the peak of the mountain will be shining under sunshine. High quartz content in rocks is the reason for this uniqueness. It reflects the sunshine like golden beam. The quartz contents range up to 83% from an old investigation. And fossils can be found at the area of Jinmianshan.

What to do with this earthcache?

Expand knowledge of rock types in the area of Jinmianshan, differentiating sandstone and shale. Recognize sedimentary layer in Taipei Basin. Discover and classify the fossil. Observe the shape of mountain and make some classification.

Task One: recognize rocks, fossils, and Formations

Geological properties at Jinmianshan

In geology, there are two main underlying Formations at the area of Jinmianshan, Mushan Formation and Wuchihshan Formation. Wuchihshan Formation and Mushan Formation are sedimentary layers. Wuchihshan Formation was formed earlier than Mushan Formation. Hence, Wuchihshan Formation is under Mushan Formation.

Wuchihshan Formation belongs to Oligocene. And it was formed at 30 MA to 23 MA before. It is the oldest discovered formation in Taipei Basin. The main rock type in this layer is sandstone.

Mushan Formation was formed from late Oligocene to Miocene, about 24 MA to 22MA before. The main rock types are sandstone and shale. Coal mining activity was lively in Taipei and New Taipei city. Mushan Formation has a layer of Coal Formation. It was the key point to the coal mining industry in early Taiwan.

Along the Jinmianshan hiking trail, sedimentary rocks like sandstone and shale can be observed.

Shale is a fine-grained, clastic sedimentary rock. Particles in the shale are much smaller than sandstone. It is characterized by fissility, which means the ability to split along flat planes of the weakness. Tactile feeling (depends on different people) of shale is less grained.

Sandstone is clastic sedimentary rock mainly composed of sand-sized (0.0625 to 2 mm) particles. Most sandstone is composed of quartz, feldspar and lithic fragment. They have good resistance to weathering process. Tactile feeling of sandstone is more grained due to sand-sized particle. Feeling, however, depends on different people.

Fossil on the peak of Jinmianshan

From the analysis of Formations, the composition of rocks, and the discovered fossils, Wuchihshan Formation and Mushan Formation are supposed to be formed at the environment of underwater. Some fossils can be discovered at the peak of Jinmianshan. They may be the evidence to the assumption.

Let’s expand some knowledge of body fossil and trace fossil.

Body fossil are the remains of the body parts of the ancient creatures. It presents with actual bones and figures. On the other side, trace fossil provides the evidence of the movements or activities of the ancient creatures by presenting traces, footprints, boring, or caves. Body fossil tells the figure of creatures ever in the world and trace fossil tells how the creatures ever living in the world.

Examples from the picture above demonstrate body fossil and trace fossil.

Body Fossil

The ancient creatures of the body fossil are Nautilus (left) and sea urchin (right).

Trace Fossil

The left and middle example of trace fossil show the movement on the surface of sediment and dwelling cave respectively. They have some evidences for activities underwater or at littoral zone. The right example of trace fossil is footprint and shows the movement on the land.


Task Two: knowing the types of mountain

Jinmianshan’s height is 258 meters. It was formed into a mountain by some geological activities. Let’s expand knowing about the formation and classification of mountain from this earthcache. Then, classify the possible formation for Jinmianshan.

Classification of mountain

Generally, mountain can be classified as fault-block mountain, fold mountain, volcanic mountain, and dome mountain. Some mountains are classified by other geological forming reason, such as plateau mountains, uplifted passive margin, upwarped mountain, and hotspot mountains. All the mountains on Earth are shaped by erosion and weathering.

Fault-Block Mountain

Fault-Block Mountain is related to fault. From the picture below, rocks endure pressures. As the pressures grow, rocks would break along the fault. Blocks get pushed up or down. Then Fault-Block Mountain is formed due to the drop caused by the drop between these blocks.

Fault-Block Mountain can be massive. However, they are not as big as fold mountains. This might be the geological processes of fault are in a relatively smaller scale and involve less pressure. They are not easy to recognized while lacking the information of faults or geological activities. From their appearance, they generally have a steep side and a side in slow slope.

Fold Mountain

Fold Mountain is related to orogeny. Plates collide each other at the convergent boundary. If they are not in similar density, plate with high density would sink down and the other would rise due to lower density. On the other hand, plates with similar density collide each other causing no one sinking. The collision generates upward force. Lithospheres underlying crumble and appear to be folded. Then, the mountains are shaped by erosion effect. See the picture below.

Fold Mountains do not occur at the tectonic edges. Instead, the fold process can take place inside a tectonic plate. Fold process occurs at the collision of plates whether they are in similar density or not. Fold Mountains are usually massive due to tectonic activity. It can be over thousands of kilometers. Fold Mountains are common on Earth, like the Himalaya or the Alps.

Volcanic Mountain

Volcano is a type of mountain. The reason for the volcanic mountain is that magma rises up through the crater. They can be eruptive or flowing slowly. Volcanic lava cools down, solidifying and piling up into a mountain. Fuji Mountain is a classic example of volcanic mountain. Datun Mountain in Taipei is also a good example of volcanic mountain.

Dome Mountain

Dome Mountain is also related to magma. But it is not volcano. Magma sometimes is accumulated underneath the surface. The magma cools down and solidifies under Erath surface. It is often harder than surrounding rocks. It is exposed by differential erosion effect. Half Dome in the Sierra Nevada Range is a good example of dome mountain. 


















實體化石圖例中的遠古生物為鸚鵡螺 (左) 與海膽 (右)。


生痕化石圖例呈現生物在沉積物表層移動的痕跡 (左) 與鑿洞穴 (中間),他們提供水底活動或是濱海地區的一些證據。右方的生痕化石圖例為足跡,顯現生物曾在陸地上移動。





山的形成大致有四種主要類型,斷塊山、褶曲山、火山、穹丘山,依不同的地質活動,還有其他的分類類型,像是高原山、上升大陸邊緣、upwarped mountain、hotspot mountain。地球上所有的山都受到侵蝕與風化的作用塑形。












Flag Counter


Task One: recognize rocks, fossils, and Formations

Waypoint I: beginning of the hiking trail

1.1 Compare the rocks at A and B. Are they the same type of rock? 1.2 Interpret your answer.

Waypoint II: the peak of Jinmianshan


Fossils can be discovered at the area. Compare the fossil in area C and the picture demonstrated in the listing page.

2.1 What's the possilble environment when this fossil was formed? (Land or Underwater)

2.2 What's the type of the base rock of the fossil? Interpret your obsevation.

Wuchishan and Mushan Formation are sedimentary layers under Taipei. The main rock in Wuchihshan Formation is sandstone. The main rocks in Mushan Formation are sandstone and shale. Wuchihshan Formation is older than Mushan Formation. Hence, Wuchihshan Formation should be under Mushan Formation. Base on the observation on rocks at wayppoint I & II.

3.1 The possible Formation at the peak of Jinmianshan (waypoint II) is Mushan Formation. (True/False) 

3.2 The possible Formation at the peak of Jinmianshan is the younger one. (True/False)

3.3 Explain why or why not in question 3.2.

Task Two: knowing the types of mountain

4.1 What’s the possible type of Jinmianshan?

4.2 Interpret your classification.

5. Explore the peak of Jinmianshan. Photo it with you, your identity items, or your GPS device.

Log this cache "Found it" and send me your suggested answers either via my profile, or via (Message Center) messaging, and I will contact you if there is a problem.




1.1 比較A處和B處的岩石,請問他們是相同類型的岩石嗎? 1.2解釋你的判斷。




2.1 區域C的化石成形時,可能是怎樣的環境? (陸地或水下)

2.2 看看四周,化石的岩體可能是什麼類型的岩石? 解釋你的觀察?


根據waypoint I & II的岩石觀察。

3.1 金面山頂(地點二)的地層是木山層? (True/False)

3.2 山頂的地層年代比較年輕。(True/False)

3.3 解釋3.2的判斷。


4.1 金面山比較可能是哪一種類型的山?

4.2 解釋你的答案。

5. 探索金面山山頂,與你、你的代表物、或GPS拍照。




內湖清代採石場 from wiki

Mountain Formation from wiki

The main types of mountains by Mihai Andrei  February 15, 2019 in Feature Post, Geology, Science ABC

Sandstone from wiki

Shale form wiki

Additional Hints (Decrypt)

Gjb-fgntr rnegupnpur

Decryption Key


(letter above equals below, and vice versa)