August 10th, 2019. This list is now long out of date. Fully 30% of links die each year on the net, making any link article impossible to maintain.
These publications offer a clear path for submitting article proposals.
Discover Magazine: http://discovermagazine.com/magazine/contact
Esquire Magazine. Unusual. Accepts complete manuscripts. Link now dead. http://esquiresubmissions.com
Harpers: http://harpers.org/submissions/
High Country News: http://www.hcn.org/about/submissions
Los Angeles Times Magazine: http://www.latimes.com/la-tm-guidelines,0,760705.story#axzz2slBY9koC
Pacific Horticulture Magazine: http://www.pacifichorticulture.org/magazine/submit/
Popular Mechanics: http://www.popularmechanics.com/about/contact-us
Popular Science: http://www.popsci.com/contact-us
Sacramento News and Review: http://www.newsreview.com/sacramento/submission_guidelines/viewpage
Sactown Magazine: http://www.sactownmag.com/Contact-Us/
Scientific American: http://www.scientificamerican.com/page.cfm?section=submission_instructions
Smithsonian Magazine: http://www.smithsonianmag.com/contact/article-submit-print-magazine/
Spirit Magazine: http://www.spiritmag.com/pdf/WritersGuidelines1.13.pdf
Sunset Magazine: http://www.sunset.com/general/travel-writers-00400000035100/
Via Magazine: http://www.viamagazine.com/about-via