This is one of several supercessions of ancient Tibetan goddesses by Buddhism, in which a royal avatar of Avalokiteśvara conquers the earth goddess Srinmo. This foundational myth is the basis for the ceremonial piercing / nailing-down of Earth in order to found a new temple or monastery. It is a symbolic subjugation of the untamed female energies of Nature by the masculine clergy.

Offerings to the Goddess Palden Lhamo, late 1500s

There is more to the underlying doctrine, beyond the symbolic subjugation of Srinmo the Earth Mother. Another Tibetan goddess is Palden Lhamo, a native goddess who was originally an enemy to Buddhism, was converted and became a Dharma Pala (Protector). She becomes a wrathful goddess, depicted above in a 16th century thangka. This is a good summary:

"She is the only female among the traditional 'Eight Guardians of the Law' and is usually depicted as deep blue in colour and with red hair to symbolise her wrathful nature, crossing a sea of blood riding side-saddle on a white mule. The mule has an eye on its left rump where her angry husband's arrow hit it after she killed her son (who was destined, and being raised to be the one to finally put an end to Buddhism) and used his skin as a saddle blanket. She has three eyes and is often shown drinking blood from a human skull."

Machik Pellha Zhiwé Nyamchen (Wylie: (or in Wylie's transliteration, ma gcig dpal lha zhi ba'i nyams can) which means "Pacified Expression of the Common Wife Palden Lhamo"), who is described as an unusually peaceful form of Palden Lhamo.

Palden Lhamo in turn oversees the Tenmas, again originally pre-Buddhist Nature goddesses:

"The Tenma goddesses are twelve guardian deities in Tibetan Buddhism. In hierarchy, they fall under Palden Lhamo, one of the eight Dharmapala deities. Other times, they are part of the retinue of the Bönpo goddess, Sidpa Gyalmo. Formerly, the 12 Tenma were said to have been local protectors of Tibet before the spread of Buddhism until they came to Padmasambhava's Asura Cave in the Pharping region of Nepal while Padmasambhava was subduing many deities and spirits. Some stories say that the goddesses were hostile to the spread of Buddhism during this time while others said that they refused to give their life essence to Padmasambhava and wanted to keep protecting Tibet. Either ways, Padmasabhava defeated them and bound them to an oath to protect the dharma.

In Dharamsala, India, there is a Tenma oracle, for which a young Tibetan woman is the kuten, which literally means, "the physical basis". 

The Twelve Tenmas

Supercession is a very strong theme in accounts of the Tenmas.. Buddhist sources often refer to them as "twelve Local deities subjugated by padmakara,” (https://www.tbrc.org/#!rid=T2524)or by Padmasabhava, the founder of Tibetan Buddhism, known as Guru Rinpoche. The milder forms say that he bound them by oath not to do harm. 

There’s a strong undercurrent of femaleness / Nature / indigeneity as inherently demonic, male / mind / Buddhist theology as superior, a thread that also runs through beliefs (doctrines!) that enlightenment can only be attained in a male body, found in many Buddhist contexts including Chinese texts around Amitofo / Amitabha. This theme leads to the feminist intervention of the Tara tradition, with her vow to only attain enlightenment in female form. So there are many layers here, and we have to look at such themes of women’s resistance as well as the dominance overlays (“their minds have been tamed”). 

This source lays out the account of oath-binding, which has imperial as well as patriarchal underpinnings: 

Guru Rinpoche was first invited to Tibet by King Trisong Detsen. At the time, the king had invited the great abbot of Nalanda named Santarakshita to build Tibet’s first monastery (Samye Monastery) and establish the order of Buddhist Sangha in the country. However, Santarakshita’s efforts were plagued by the local deities and powerful spirits such as Nechung, who were against Buddhism’s arrival. If the local populace became Buddhists, these deities would lose their human followers.

Being unable to subdue the local deities himself, Santarakshita advised King Trisong Detsen to invite the renowned Tantric master Guru Rinpoche to Tibet. Accepting the invitation, Guru Rinpoche readied himself for the coming spiritual warfare by entering powerful retreats. While he was in retreat at Asura Cave in present-day Pharping in Nepal, the Tenma Chunyi or the Twelve Tenma Goddesses, of which Dorje Geg Kyi Tso is one, advanced to attack the great tantric master using supernatural powers.

He then subjugates them, and this story displays the formal supercession of these goddesses, calling them unenlightened beings who came under the control of lamas, and toward the end gives dire warnings against working with them directly: “Below is the praise and mantra of the goddess Dorje Geg Kyi Tso. While she is not an enlightened being, therefore we do not take refuge in her, she can still provide practitioners with the help they need to overcome obstacles and advance along their spiritual path. We take refuge in Shakyamuni Buddha always and with this, we can invoke her help if we like, as she is promised to help practitioners.

Please remember that when you rely on unenlightened beings, they can cause you harm even though they are bound by oath. As they are not enlightened, their clairvoyance is limited. They can see that if you do a certain action now that it will work out well, and they have foresight into the future. However, this foresight is limited. For example, they can only see 10 years into the future, and for those 10 years they see that the action will be good. However, if you do as they advised, after 15 years perhaps this action will harm you. They did not know that it would harm you because they have limited abilities. So their harm is unintentional due to their limitations. They may indeed be bound by high lamas, or their minds have been tamed, but you can still be harmed.

Palden Lhamo, a more modern mural at Tawang Monastery

What i find most interesting on this site is that, like the Mosuo, the ancient Tibetan traditions revere lake mothers, and here’s the Nine again, in an origin story that again is concerned with the founders of Tibetan Buddhism superseding them: 

"Legend has it that Dorje Geg Kyi Tso, a celestial maiden from the heavenly realms descended and took on the form of Yamdrok Yumtso. She first appeared as nine separate lakes but Yeshe Tsogyal, the consort of Guru Rinpoche, became anxious about the lives of creatures who came to live in Yamdrok Yumtso’s waters. If the nine lakes dried up, the creatures would perish. Throwing gold into the air as an offering to all the Buddhas, making auspicious prayers and reciting sacred mantras, Yeshe Tsogyal was able to combine the lakes into one unified whole.

"The lake formed into the shape of one of Guru Rinpoche’s many ritual implements, an iron scorpion; hence many places around the basin of the lake include the word ‘scorpion’. At the heart of this scorpion shape is a small island with a Nyingma temple that was built in the 16th century. It is famous for a handprint left in a nearby rock by Guru Rinpoche himself. However, before Dorje Geg Kyi Tso was combined into one lake by Yeshe Tsogyal, she was bound under oath by Guru Rinpoche to never harm sentient beings and to protect those who are virtuous. In fact, she was not the only being to be bound by Guru Rinpoche in this manner.”