With the onset of autumn, it’s time for outdoor adventurers to start thinking about that all-important base layer. As the layer of clothing that’s closest to your body, the base garment provides insulation between your skin and other layers, keeping your body at an even temperature and wicking away moisture.

It’s early enough in the year to find sales on last year’s base layers at major sporting goods stores. At this writing, for example, REI is offering reductions of 30 to 50 percent on selected base layers for brands that include Dakine, Obermeyer, REI Co-op, and Marmot. www.rei.com

Or give a look at the many base layers on sale at Dick’s Sporting Goods. Among them: a 44 percent reduction on Columbia’s Glacial Fleece Printed Leggings for Women, and a 49 percent discount on Men’s Under Armour ColdGear Reactor Leggings. www.dickssportinggoods.com

Of course, there’s a much wider selection of current-season base layers in stores. Here are two excellent selections:

Columbia Men’s Heavyweight II Baselayer Half-Zip Long Sleeve Shirt: A heavy weight acts as a good defense against deep cold. Made with thermal waffle fabric and both Omni-HEAT and Omni-Wick technology that retains warmth and wicks away sweat. Ergonomic seams and four-way stretch raglan sleeves offers comfort and ease of movement. Sleeves have thumbholes. 85 percent polyester/15 percent elastane. Sizes Small to XXL. Comes in Azul or Black, $70. www.columbia.com

Smartwool’s Merino 250 Base Layer Pattern Quarter-Zip Top for Women: Made from warm and cozy Merino wool, this top is perfect for cold winter days. Flatlock stitching prevents seams from irritating skin, the fabric is a sun-protective UPF 50+, shoulder panels optimizes comfort under pack straps, and the top has a great look. Sizes S-XL. Comes in six colors/patterns: Lochness (shown here), Black/Charcoal, Black/Moonbeam Heather, Purple Mist, Winter White, and Woodrose/Bordeaux. $110. www.smartwool.com

In Sonoma County, Smartwool products are carried by Dick’s Sporting Goods, Fleet Street, REI, and Birkenstock Village; Columbia products can be found at McCaulou’s and Dick’s Sporting Goods.