Change the snow to dirt?

Where could we buy pieces exactly like the white ones on this "ramp" and change the snow to dirt? We aren't so much the skier type, my hubby is all about the mountain biking though! So we want to make this like a mountain bike track instead. It's the Lego city ski and climb set.

First time seriously obsessing over a Lego set

A fine addition to my collection

Star Wars collection

Shark! (Posting the image correctly this time)

Why did my instructions come fresh out the box with a gigantic stain and mound of dust in them? This is really disgusting.

Walter

Accidentaly made votrouvius fly

Been collecting for 1.5 years. Lego addiction is real..

Gotham '36 Part I

https://drive.google.com/folderview?id=1H_z6BKMsKprP5dkzdzez_2_T8s-2HoUt

All LEGO House Exclusive Sets

Finally!! I managed to get all the LEGO House exclusive sets!!! (+ 2016 employee set)