Les Bleuettes have been a dominant force at U20s level, and showed that they are just as strong in their first match of the Six Nations Women’s U21 Series.
They ran in 12 tries in all, with Trégouet notching a hat-trick with Gauyat and tighthead prop Amalia Bazola getting over twice.
Gabby Healan scored late in the first half for Wales, who will now hope to improve when they travel to Italy in Round 2.
France needed just two minutes to take the lead. Trégouet made the striding break out of her own half before finding centre partner Gauyat who sprinted home.
The visitors were looking very dangerous and added a second try on seven minutes, tighthead prop Bazola showing her power to get outside and through a defender and dot down. Mae Levy converted and made it 12-0.
Having been on the back foot for much of the first 10 minutes, Wales responded with some extended possession, doing everything to break down the visitors.
But they could not find a way through and instead, it was France who got a third try. Fly-half Garance Merle wreaking havoc with an initial break and when the ball came back left, Trégouet showed that she can score as well as create, handing off three would-be tacklers on her way to the line. From the touchline Levy converted and made it 19-0.
And after Alice Grandhomme had broken clear down the right, France punished a Welsh indiscretion, Lylou Pedussaud with a tap penalty and offload for Gauyat's second of the evening. Levy converted once more.
France lost back-rower Anais Peralez to the sin-bin for persistent offending and Wales almost made them pay, Gwennan Hopkins held up over the line before the Welsh skipper almost got in again, breaking the line only to be hauled down five metres short and isolated, conceding a penalty in the process.
Wales finally did get over on the stroke of half-time though, Healan taking advantage of Levy failing to gather a cross-kick with the sun in her eyes, with the winger somehow getting the ball down despite two defenders trying to force her out.
But France finished the half the stronger, Trégouet scoring her second with a searing run through the midfield, shaking two tacklers on her way to the line, before Grandhomme completed a long-range counter-attack, racing home from 60 metres out, fending off two would-be tacklers on her way to the line.
Leading 40-5 at the break, France extended their lead early in the second half, Elina Folituu getting over from a rolling maul.
And just as she had in the first half, Bazola got over for the second try of the second half, finishing after Peralez had been stopped just short of the line. Gauyat took over kicking duties from Levy and converted to stretch the lead to 52-5.
Trégouet was causing the Welsh defence problems every time she got the ball and made another break to put Iness Zeze over.
She followed that up with her best of the day, running from her own half down the left touchline, stepping and fending her way to a hat-trick. Gauyat converted and France led 64-5.
France were looking so dangerous and when Aneymone Talalua, Grandhomme collected before returning the ball to the replacement to score. Gauyat's conversion took them past 70.
Wales lost fly-half Hanna Marshall to the sin-bin for an intentional knock-on four minutes from time, with Maiana Gony taking advantage as Trégouet featured twice in the build-up to round off the win.