Replying to myself, just to bring closure:

Summary. --The Small Sugar pumpkin has a rooting habit somewhat similar to that of the Hubbard squash. Three-weeks-old plants have taproots which penetrate downward at the rate of 1 inch per day. Major branches occur only in the first 8 inches of soil. The longest extends horizontally nearly 2 feet. By midsummer the strongly branched vines are over 7 feet long and have 75 square feet of leaf surface. The rather crooked taproot has doubled in length. Below the surface foot the root network does not exceed 8 to 24 inches in lateral extent. But in the foot of surface soil the strong laterals, usually about 10 in number, spread outward 3 to 8 feet. Those of lesser spread often turn downward into the second and third foot and all give rise to vertically descending laterals, frequently in great abundance. Both main roots and their branches are so thoroughly furnished with rootlets that not only the surface soil but, to a lesser extent, the second and third foot as well are also fully occupied.

Maturing plants, with vines 16 feet in length, have taproots extending to the 6-foot level. The portion of the root system originating from the taproot below 12 inches makes relatively a small growth when compared with that in the shallower soil. The major surface laterals (usually 6 to 10 in number) are often ¼ inch thick and extend outward in rather devious courses 5 to 17.5 feet. Branched throughout their course at the rate of four to eight laterals per inch, many of which are 2 to 4 feet long and all complexly and minutely rebranched, they form a wonderfully efficient root complex. It is even more profuse than that of the squash and like it still grows rapidly. The obliquely penetrating roots extend into the fourth foot of soil. These and the very numerous vertical branches are features not found or at least not prominent in the squash. Descending into the second and third foot in great numbers and often at a distance of 6 feet from the base of the plant, laterals penetrating vertically downward thoroughly ramify the deeper soil. Nodal root development is similar to that of the squash.

Here is a link that might be useful: Root development of pumpkins