In Rig Veda, it was not mentioned that Indra cut off the wings of mountains. It simply says Indra stabilised the wavering Earth and quaking mountains.
यः पृथिवीं व्यथमानामदृंहद्यः पर्वतान्प्रकुपिताँ अरम्णात् । यो अन्तरिक्षं विममे वरीयो यो द्यामस्तभ्नात्स जनास इन्द्रः ॥
yaḥ pṛthivīṃ vyathamānām adṛṃhad yaḥ parvatān prakupitām̐ aramṇāt | yo antarikṣaṃ vimame varīyo yo dyām astabhnāt sa janāsa indraḥ ||English translation:
Who made firm the wavering earth, who settled the quaking mountains, who gave the midspace/antarikṣaṃ ider measure, who propped up the heaven – he, o peoples, is Indra.
===
Actually, if understood esoterically, Indra is the Illuminated DIVINITY.
In spiritual practices, Indra assists the spiritual practitioner in stabilising the wavering MIND (Earth), after annihilating the deep rooted vices (subduing mountains), and clearing the path for the practitioner the mid-space or antarikṣa and finally, pushing the practitioner towards the final realm - the Heaven.
===
The scholars of subsequent periods, without understanding this spiritual connotation of the above Rik, created a story of Indra cutting off the wings of mountains in Maitrāyaṇī Saṃhitā (i, 10, 13).
indraḥ pakṣān achinat tair imām adṛṃhad - "Indra cut off their wings. With those [severed wings], he made this [earth] firm and steady."
====
In Ramayana, the same narration was carried out, duly adding some spices to the story and incorporated in the 1st Sarga of Sundara Kanda.
Minaka, a mountain with wings, was stated to have been saved by Vayu, when Indra was cutting off the wings of all mountains, and dropped him in the ocean. Minaka narrates this story to Shri Hanuman.
It is an interpolated story, but not from original Ramayana.
पूर्वं कृतयुगे तात पर्वताः पक्षिणोऽभवन् |
ते हि जग्मुर्दिशः सर्वा गरुडानिलवेगिनः || ५-१-१२३"O son! Earlier in the Krita yuga, mountains had wings. With speed equal to that of Garuda and Vayu, they went in all directions."
ततस्तेषु प्रयातेषु देवसंघः सहर्षिभिः |
भूतानि च भयं जग्मुस्तेषां पतनशङ्कया|| ५-१-१२४"After that when those mountains were thus flying freely, Devas and living creatures together with sages obtained fear in the doubt that those mountains might fall down."
ततः क्रुद्धः सहस्राअक्षः पर्वतानां शतक्रतुः |
पक्षान् चिच्छेद वज्रेण तत्र तत्र सहस्रशः ||५-१-१२५"Then the angry Devendra who performed a hundred Asvamedha rituals, cut off the wings of thousands of mountains by his weapon vajra then and there."
स मामुपागतः क्रुद्धो वज्रमुद्यम्य देवराट् |
ततोऽहं सहसा क्षिप्तः स्वसनेन महात्मना || ५-१-१२६"That Devendra angrily reached me with raised vajra. Then I was thrown away immediately by the great Vayu."
अस्मिन्लवणतोये च प्रक्षिप्तः प्लवगोत्तम |
गुप्तपक्षसमग्रश्च तव पित्राभिरक्षितः || ५-१-१२७"O best among vanaras! With saved full wings, being thrown down into this salt ocean, I have been protected by your father."
