Paul identifies Jesus Christ as the "spiritual Rock" [πνευματικης. . .πετρας] who followed Israel in the wilderness:

Rabbinic Legends

Later Rabbis told folk tales about how a beehive-shaped rock went bouncing along behind the children of Israel in their wilderness journeys. One version of the tale even features a completely formed well that goes tromping along up hill and dale. If such fables existed in his day and if Paul ever heard them, he rules out this carnal understanding by calling Christ the "spiritual Rock" [πνευματικης. . .πετρας] who followed Israel in the wilderness. The Rabbis' physical rock is not here in view.

"By spiritual we are to understand that which is divine or supernatural. . .There is a Jewish tradition to the effect that a fragment was broken off the rock that Moses smote and that this accompanied the Israelites through their wanderings, a tradition Paul used by way of illustration. But that the stream from the rock did not journey is proven by another smitten rock at Kadesh (Num. 20:1, 7-13). The qualifying phrase in Paul's rehearsal of the wilderness experiences is that Rock was Christ. He was the spiritual rock who followed a redeemed people." (All the Messianic Prophecies of the Bible, by Herbert Lockyer, p. 313).

Before and Behind

God in the person of the Angel of the Lord went before the children of Israel in the Wilderness. God is both the avant-garde, and also the rear-guard:

"For you shall not go out with haste, Nor go by flight; For the Lord will go before you, and the God of Israel will be your rear guard." (Isaiah 52:12).

"Then your light shall break forth like the morning, Your healing shall spring forth speedily, And your righteousness shall go before you; The glory of the Lord shall be your rear guard." (Isaiah 58:8).

To put it another way, "The angel of the LORD encampeth round about them that fear him, and delivereth them." (Psalm 34:7).

"In most cases, He went before them, and when occasion required it, He followed behind (Exod. 14:19). If the Angel God sent to accompany the people and whose voice they were commanded to  obey represents a theophanic appearance of Christ, then He was the rock who acted as a fellow-traveler with Israel (Exod. 23:20-23)." (All the Messianic Prophecies of the Bible, by Herbert Lockyer, p. 313).

The Rock of Israel

If we simply play the percentages in guessing what Paul means by the 'rock,' what are the results? Certainly much of the time a rock is just a rock. God commanded Moses to smite the rock at Horeb, promising that He would stand upon it:

"And the LORD said unto Moses, Go on before the people, and take with thee of the elders of Israel; and thy rod, wherewith thou smotest the river, take in thine hand, and go. Behold, I will stand before thee there upon the rock in Horeb; and thou shalt smite the rock, and there shall come water out of it, that the people may drink. And Moses did so in the sight of the elders of Israel." (Exodus 17:5-6)

Yet often God Himself is the rock:

What does 'rock' mean in this connection? There seems to be some suggestion of origin, as Maimonides pointed out: "The word zur (rock) is a homonym. First, it denotes 'rock,' as 'And thou shalt smite the rock' (zur) (Exod. xvii. 6). . .It is next employed to signify the quarry from which the stones are hewn: comp . 'Look unto the rock (zur) whence ye are hewn' (Isa. li. 1). From this latter meaning of the term another figurative notion was subsequently derived, viz., 'the root and origin' of all things." (Moses Maimonides, Guide to the Perplexed, p. 34). In addition there is the idea of strength and preservation, as in a stronghold.

These 'God is our rock' references are plentiful, in fact a plurality of all Old Testament uses of the word 'tsur' fall into this category:

Sometimes the translators get the idea across by going back to the underlying thought of a rock, of stability, strength and immovability:

"Let the words of my mouth, and the meditation of my heart, be acceptable in thy sight, O LORD, my strength ['tsur,' 'rock'], and my redeemer." (Psalm 19:14).
"Let the sayings of my mouth, And the meditation of my heart, Be for a pleasing thing before Thee, O Jehovah, my rock, and my redeemer!" (YLT, Psalm 19:14).

"Be thou my strong ['tsur,' 'rock'] habitation, whereunto I may continually resort: thou hast given commandment to save me; for thou art my rock and my fortress." (Psalm 71:3).
"Be to me for a rock — a habitation, To go in continually, Thou hast given command to save me, For my rock and my bulwark art Thou." (YLT, Psalm 71:3).

"My flesh and my heart faileth: but God is the strength ['tsur,' 'rock'] of my heart, and my portion for ever." (Psalm 73:26).
"Consumed hath been my flesh and my heart, The rock of my heart and my portion is God to the age." (YLT, Psalm 73:26).

"Trust ye in the LORD for ever: for in the LORD JEHOVAH is everlasting strength  ['tsur,' 'rock']: For he bringeth down them that dwell on high; the lofty city, he layeth it low; he layeth it low, even to the ground; he bringeth it even to the dust." (Isaiah 26:4-5).
"Trust ye in Jehovah for ever, For in Jah Jehovah is a rock of ages, For He bowed down the dwellers on high, A city set on high He maketh low, He maketh it low unto the earth, He causeth it to come unto the dust. . ." (YLT Isaiah 26:4).

"Ye shall have a song, as in the night when a holy solemnity is kept; and gladness of heart, as when one goeth with a pipe to come into the mountain of the LORD, to the mighty One  ['tsur,' 'rock'] of Israel." (Isaiah 30:29).
"Singing is to you as in a night sanctified for a festival, And joy of heart as he who is going with a pipe, To go in to the mountain of Jehovah, Unto the rock of Israel." (YLT Isaiah 30:29).

"Art thou not from everlasting, O LORD my God, mine Holy One? we shall not die. O LORD, thou hast ordained them for judgment; and, O mighty God ['tsur,' 'rock'], thou hast established them for correction." (Habakkuk 1:12).
"Art not Thou of old, O Jehovah, my God, my Holy One? We do not die, O Jehovah, For judgment Thou hast appointed it, And, O Rock, for reproof Thou hast founded it." (YLT, Habakkuk 1:12).

Another word meaning 'cliff' or high and lofty rock is also sometimes used of God, "The LORD is my rock , and my fortress, and my deliverer; my God, my strength, in whom I will trust; my buckler, and the horn of my salvation, and my high tower." (Psalm 18:22), and "I will say unto God my rock, Why hast thou forgotten me? why go I mourning because of the oppression of the enemy?" (Psalm 42:9).

Smite the Rock

Moses was commanded to smite the rock at Horeb, though later at Kadesh he was told to speak to the rock:

"And the LORD spake unto Moses, saying, Take the rod, and gather thou the assembly together, thou, and Aaron thy brother, and speak ye unto the rock before their eyes; and it shall give forth his water, and thou shalt bring forth to them water out of the rock: so thou shalt give the congregation and their beasts drink. And Moses took the rod from before the LORD, as he commanded him. And Moses and Aaron gathered the congregation together before the rock, and he said unto them, Hear now, ye rebels; must we fetch you water out of this rock? And Moses lifted up his hand, and with his rod he smote the rock twice: and the water came out abundantly, and the congregation drank, and their beasts also. And the LORD spake unto Moses and Aaron, Because ye believed me not, to sanctify me in the eyes of the children of Israel, therefore ye shall not bring this congregation into the land which I have given them." (Numbers 20:7-12).

All of these things were crafted by God as word pictures to instruct and foretell as well as to quench the people's thirst. Moses' upheld hands cast a long shadow in the setting sun. The smitten rock is a type of Christ:

God was present in this miracle: "Tremble, thou earth, at the presence of the Lord, at the presence of the God of Jacob; Which turned the rock into a standing water, the flint into a fountain of waters." (Psalm 114:7-8), indeed the psalmist says it was His presence which produced the miracle.

"Here we have a plain prophecy and picture of Christ, the rock of ages, smitten of God for our iniquities. Water was promised from the smitten rock: 'There shall come water out of it that the people may drink;' and from the riven side of Jesus there flowed the double cure from sin's guilt and power. . .It was predetermined that from the smitten Lamb of God streams of grace would gush forth to refresh and quicken a lost world. Cleft by the hand of Jehovah at Calvary, the stricken Lamb opened the floodgates of love." (All the Messianic Prophecies of the Bible, by Herbert Lockyer, p. 310).

Christ is the smitten one: "I gave my back to the smiters, and my cheeks to them that plucked off the hair: I hid not my face from shame and spitting." (Isaiah 50:6). And from Him flows the fountain of living water.

Cleft in the Rock

God commanded Moses to shelter in the cleft of a rock:

"And the LORD said, Behold, there is a place by me, and thou shalt stand upon a rock: And it shall come to pass, while my glory passeth by, that I will put thee in a clift of the rock, and will cover thee with my hand while I pass by: And I will take away mine hand, and thou shalt see my back parts: but my face shall not be seen." (Exodus 33:21-23).

There is a lovely song which develops this theme:

A 'rock' is a fortress, a place of protection from all threats of harm. This idea of God as the rock, i.e. the strong tower of the faithful, is developed at length in the psalms:

“'He only is my rock and my salvation.' Sometimes a metaphor may be more full of meaning and more suggestive than literal speech; hence the use of the figure of a rock, the very mention of which would awaken grateful memories in the Psalmist’s mind. David had often lain concealed in rocky caverns, and here he compares his God to such a secure refuge; and, indeed, declares him to be his only real protection, all-sufficient in himself and never failing.”
(Spurgeon, Charles. Psalm 62, The Treasury of David (Kindle Locations 31119-31122). GLH Publishing.)

In military experience, there are many secure rocky heights which can server as inaccessible citadels for a band of men. None of the weaponry available in antiquity could shatter a solid rock. The idea of the "only" rock, as in Psalm 62, seems to bleed over from monotheism; for the believer, God is not 'a' rock, but the "only" rock:

The Wisdom of God

Philo Judaeus identified the 'flinty rock' from which water gushed as the wisdom of God. (Philo also understands the wisdom of God to be the word of God):

"To return to what I was saying, the soul falls in with a scorpion. . .until God send forth the stream from His strong wisdom and quench with unfailing health the thirst of the soul that had turned from Him. For the flinty rock is the wisdom of God, which He marked off highest and chiefest from His powers, and from which He satiesfies the thirsty souls that love God. And when they have been given water to drink, they are filled also with the manna, the most generic of substances, for the manna is called 'somewhat,' and that suggests the summum genus. But the primal existence is God, and next to Him is the Word of God, but all other things subsist in word only, but in their active effects they are in some cases as good as non-subsisting." (Philo Judaeus, Allegorical Interpretation, II, Chapter XXI, p. 270 Loeb edition).

It is not difficult to trace the connection between wisdom and the flowing fount of water, for instance in Proverbs, "The words of a man’s mouth are as deep waters, and the wellspring of wisdom as a flowing brook." (Proverbs 18:4), or "Understanding is a wellspring of life unto him that hath it: but the instruction of fools is folly." (Proverbs 16:22). At this distance in time no one can know how much of a 'lone ranger' Philo was, whether his ideas were mainstream commonplaces or exotic. This well of water springing up continues flowing into the New Testament: "But whosoever drinketh of the water that I shall give him shall never thirst; but the water that I shall give him shall be in him a well of water springing up into everlasting life." (John 4:14), "He that believeth on me, as the scripture hath said, out of his belly shall flow rivers of living water." (John 7:38). Certainly the thirst the children of Israel experienced was literal enough, as was the water which quenched it, but there was also a deeper dimension. Realizing that the manna, the bread from heaven, and the water from the rock, then it is easy enough to see who Jesus is claiming to be when He ascribes all these titles to Himself:

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Philo Judaeus

Stone of Stumbling

One very direct statement of the deity of Jesus Christ which fits into our theme is the stone of stumbling:

"Sanctify the LORD of hosts himself; and let him be your fear, and let him be your dread. And he shall be for a sanctuary; but for a stone of stumbling and for a rock of offence to both the houses of Israel, for a gin and for a snare to the inhabitants of Jerusalem.  And many among them shall stumble, and fall, and be broken, and be snared, and be taken." (Isaiah 8:13-15).

Isaiah's stone of stumbling is "the LORD of hosts himself." Peter's is the Lord Jesus Christ:

"Wherefore also it is contained in the scripture, Behold, I lay in Sion a chief corner stone, elect, precious: and he that believeth on him shall not be confounded. Unto you therefore which believe he is precious: but unto them which be disobedient, the stone which the builders disallowed, the same is made the head of the corner, and a stone of stumbling, and a rock of offence, even to them which stumble at the word, being disobedient: whereunto also they were appointed." (1 Peter 2:6-8).

How Many Rocks?

It's fair to say that we could count very many rocks scattered about down in the Grand Canyon, those being physical rocks, but in our sense, in Paul's sense of the "spiritual Rock" [πνευματικης. . .πετρας], how many rocks are there? Not so many:

In addition to the common rocks scattered about the quarries, there is also a metaphorical use of the word 'rock,' as for instance when men are said to be 'rocks,' owing to their constancy or stolidity, such as Abraham: "Hearken to me, ye that follow after righteousness, ye that seek the LORD: look unto the rock whence ye are hewn, and to the hole of the pit whence ye are digged." (Isaiah 51:1), or Peter. But the use of this term applied to God is not a metaphor, i.e. 'figurative' as opposed to 'literal,' if the guiding idea of a 'rock' is strength and perdurance. These qualities 'literally' pertain to God in a pluperfect way not attainable by the frangible, readily fractured aspirants to 'rockhood' laying about the quarry.

In calling Jesus the "spiritual" rock, Paul removes Him from the plentiful quarry category of rocks, the Rabbis to the contrary notwithstanding. Then into what category is He thrust: the 'rocks' of whom the living God says there is only One? "Their rock," the false gods, cannot add any increment to the god-census. It is precisely this category, 'spiritual rock,' which is limited to one entry. Or can the Christian not repeat with David, "He only is my rock and my salvation" (Psalm 62:2)? Then Jesus is the Rock of Ages. Who is the sole spiritual rock of Israel? It is the living God and none other.